Perch Members Reset Password Form nukes MAMP's email sending ability(?)

I'm totally puzzled why this is happening, but the 'Perch Members' app seems to break MAMP's ability to send emails—specifically, as soon as I submit a 'reset password' form on the front-end. I wonder if my problem is related to this post too: https://forum.grabaperch.com/forum/03-24-2016-perch-members-reset-password-default-form-not-sending-email

Could you see any reason why this would happen? It has happened to me twice now in the last 24 hours, and I can't come to any other conclusion as to the cause.

I was only able to recover by completely re-installing my OS (macOS High Sierra), but it's broken again now that I've submitted a reset password form again via a page generated by the Members App.

Things I've tried, to recover:

• Turn my computer off and on again—always the first test ;-)
• Sending mail through postfix and mailtrap — nothing seems to get sent
• Setting up a new database and install, with nothing else other than a config file and Perch core files
• Uninstalling MAMP, then re-installing it
• Upgrading MAMP (went from v4, to v5)

I've checked the mysql_error.log and see this:

Version: '5.7.21'  socket: '/Applications/MAMP/tmp/mysql/mysql.sock'  port: 3306  MySQL Community Server (GPL)
2018-08-16T23:40:39.927608Z 3 [Note] Access denied for user 'jaygeorge'@'localhost' (using password: NO)
2018-08-16T23:40:39.927633Z 2 [Note] Access denied for user 'jaygeorge'@'localhost' (using password: NO)
2018-08-16T23:40:39.927679Z 4 [Note] Access denied for user 'jaygeorge'@'localhost' (using password: NO)
2018-08-16T23:40:39.940007Z 5 [Note] Access denied for user 'jaygeorge'@'localhost' (using password: NO)

Here are my Perch Runway diagnostics:

Perch Runway LTM: 3.1.2
Production mode: Production (100)
Installed apps: content (3.1.2), assets (3.1.2), categories (3.1.2)
DB driver: PDO
DB tables: perch3_backup_plans (0), perch3_backup_resources (0), perch3_backup_runs (0), perch3_categories (0), perch3_category_counts (0), perch3_category_sets (0), perch3_collection_index (0), perch3_collection_items (0), perch3_collection_revisions (0), perch3_collections (0), perch3_content_index (0), perch3_content_items (0), perch3_content_locks (0), perch3_content_regions (0), perch3_menu_items (8), perch3_navigation (0), perch3_navigation_pages (0), perch3_page_routes (0), perch3_page_templates (7), perch3_pages (5), perch3_resource_log (0), perch3_resource_tags (0), perch3_resources (0), perch3_resources_to_tags (0), perch3_settings (13), perch3_user_passwords (0), perch3_user_privileges (27), perch3_user_role_buckets (0), perch3_user_role_privileges (2), perch3_user_roles (2), perch3_users (1)
Users: 1
App runtimes:
<?php
    $apps_list = [ 
    ];
Editor plug-ins:
H1: 999c1ad26e106f0311f329aabcceed5f
L1: a08dfb1ac4db9f10bc7e29ff838d7ce0
F1: 3b606135b33e6a102526838f4152a807
headerColour: rgb(54,54,54)
content_singlePageEdit: 1
helpURL:
siteURL: /
hideBranding: 0
content_collapseList: 1
lang: en-gb
installedAt: 3.1.2
update_3.1.2: done
headerScheme: dark
update_runway_3.1.2: done
latest_version:
on_sale_version: 3.1.2
PERCH_DEVELOPMENT: 10
PERCH_STAGING: 50
PERCH_PRODUCTION: 100
PERCH_SITEPATH: /Users/jaygeorge/Sites/test
PERCH_SCHEDULE_SECRET: ndGPZRQWjn551dRk
PERCH_DB_USERNAME: root
PERCH_DB_SERVER: localhost
PERCH_DB_DATABASE: test
PERCH_DB_PREFIX: perch3_
PERCH_EMAIL_FROM: contact@jaygeorge.co.uk
PERCH_EMAIL_FROM_NAME: jay jay
PERCH_LOGINPATH: /perch
PERCH_PATH: /Users/jaygeorge/Sites/test/perch
PERCH_CORE: /Users/jaygeorge/Sites/test/perch/core
PERCH_RESFILEPATH: /Users/jaygeorge/Sites/test/perch/resources
PERCH_RESPATH: /perch/resources
PERCH_HTML5: 1
PERCH_TZ: UTC
PERCH_RUNWAY: 1
PERCH_ERROR_MODE: DIE
PERCH_DATE_LONG: %d %B %Y
PERCH_DATE_SHORT: %d %b %Y
PERCH_TIME_SHORT: %H:%M
PERCH_TIME_LONG: %H:%M:%S
PERCH_RUNWAY_ROUTED:
PERCH_STRONG_PASSWORDS:
PERCH_ASSET_VERSION: 6738d5d5f5664f7c5e34
PERCH_DEBUG:
PERCH_PREVIEW_ARG: preview
PERCH_TEMPLATE_PATH: /Users/jaygeorge/Sites/test/perch/templates
PERCH_TEMPLATE_FILTERS:
PERCH_DEFAULT_DOC: index.php
PERCH_DEFAULT_EXT: .php
PERCH_PRODUCTION_MODE: 100
PERCH_XHTML_MARKUP:
PERCH_RWD: 1
PERCH_HTML_ENTITIES:
PERCH_SSL:
PERCH_STRIPSLASHES:
PERCH_PROGRESSIVE_FLUSH: 1
PERCH_PARANOID:
PERCH_FORCE_SECURE_COOKIES:
PERCH_DEFAULT_BUCKET: default
PERCH_TRANSLATION_ASSIST:
PERCH_PASSWORD_MIN_LENGTH: 6
PERCH_MAX_FAILED_LOGINS: 10
PERCH_AUTH_LOCKOUT_DURATION: 1 HOUR
PERCH_VERIFY_UPLOADS:
PERCH_PRIV_ASSIST:
PERCH_CUSTOM_EDITOR_CONFIGS:
PERCH_ENABLE_EXIF: 1
PERCH_AUTH_PLUGIN:
PERCH_DB_CHARSET: utf8
PERCH_DB_PORT:
PERCH_DB_SOCKET:
PERCH_APPS_EDITOR_PLUGIN: markitup
PERCH_APPS_EDITOR_MARKUP_LANGUAGE: markdown
Hosting settings
PHP: 7.2.7
Zend: 3.2.0
OS: Darwin
SAPI: apache2handler
Safe mode: not detected
MySQL client: mysqlnd 5.0.12-dev - 20150407 - $Id: 38fea24f2847fa7519001be390c98ae0acafe387 $
MySQL server: 5.7.21
Free disk space: 195.30 GB
Extensions: Core, date, libxml, openssl, pcre, sqlite3, zlib, bcmath, bz2, calendar, ctype, curl, dom, hash, fileinfo, filter, ftp, gd, SPL, iconv, intl, json, ldap, mbstring, session, standard, mysqlnd, PDO, pdo_mysql, pdo_sqlite, Phar, posix, Reflection, mysqli, SimpleXML, soap, sockets, sodium, exif, tokenizer, wddx, xml, xmlreader, xmlwriter, xsl, zip, apache2handler, imap, gettext, pgsql, pdo_pgsql, imagick
GD: Yes
ImageMagick: Yes
PHP max upload size: 32M
PHP max form post size: 8M
PHP memory limit: 128M
Total max uploadable file size: 8M
Resource folder writeable: Yes
Session timeout: 24 minutes
Native JSON: Yes
Filter functions: Yes
Transliteration functions: Yes
HTTP_HOST: test.loc
HTTP_CONNECTION: keep-alive
HTTP_UPGRADE_INSECURE_REQUESTS: 1
HTTP_DNT: 1
HTTP_USER_AGENT: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36
HTTP_ACCEPT: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
HTTP_REFERER: https://test.loc/perch/core/settings/diagnostics/
HTTP_ACCEPT_ENCODING: gzip, deflate
HTTP_ACCEPT_LANGUAGE: en-US,en;q=0.9,de;q=0.8
HTTP_COOKIE: PHPSESSID=27o1onjg480gubec94a9onc5j0; cmsa=1
PATH: /usr/bin:/bin:/usr/sbin:/sbin
SERVER_SOFTWARE: Apache
SERVER_NAME: test.loc
SERVER_ADDR: ::1
SERVER_PORT: 80
REMOTE_ADDR: ::1
DOCUMENT_ROOT: /Users/jaygeorge/Sites/test
SERVER_ADMIN: you@example.com
SCRIPT_FILENAME: /Users/jaygeorge/Sites/test/perch/core/settings/diagnostics/index.php
REMOTE_PORT: 51573
GATEWAY_INTERFACE: CGI/1.1
SERVER_PROTOCOL: HTTP/1.1
REQUEST_METHOD: GET
QUERY_STRING: extended
REQUEST_URI: /perch/core/settings/diagnostics/?extended
SCRIPT_NAME: /perch/core/settings/diagnostics/index.php
PHP_SELF: /perch/core/settings/diagnostics/index.php
REQUEST_TIME_FLOAT: 1534463819.099
REQUEST_TIME: 1534463819
argc: 1