alphaNumeric type inconsistencies across app settings editors

From the Garmin documentation (https://developer.garmin.com/connect-iq/core-topics/app-settings/) there is no mention what characters alphaNumeric type allows. By testing with Eclipse App Settings Editor, Garmin Express Windows and Garmin Connect Mobile Android I concluded that any UTF8 character is allowed. Unfortunately today I discovered that for Garmin Express Mac and Garmin Connect Mobile iOS this is not true. Here are the results for every app setting editor (all editors were updated to the latest version):

Eclipse App Settings Editor -> Supports all UTF8 characters
Garmin Express Windows -> Supports all UTF8 characters
Garmin Express Mac -> Supports only ASCII characters
Garmin Connect Mobile Android -> Supports all UTF8 characters
Connect IQ Store Android and iOS -> Supports all UTF8 characters except: < > |
Garmin Connect Mobile iOS -> Supports all UTF8 characters except: < > & \
When using & character, the character and content after it will be removed upon saving (e.g. "ab&c" will be saved as "ab")
When using \ character, the character will be removed upon saving (e.g. "ab\c" will be saved as "abc")
When using < or > character, the whole string is cleared upon saving (e.g. "a<b" will be saved as "") and then you get redirected to an unavailable page:

For Garmin Connect Mobile iOS the following thread exists: https://forums.garmin.com/developer/connect-iq/f/discussion/5459/ios-gcm-ciq-settings-strings-do-not-accept-and-characters
but it is outdated as characters + and % are now successfully saved.

Can anyone explain why Garmin Express Mac and Garmin Connect Mobile iOS behave differently than others and what characters should be allowed by alphaNumeric type?

UPDATE:

I reported the mentioned inconsistencies:

Garmin Connect Mobile iOS not accepting <, >, & and \ characters
https://forums.garmin.com/developer/connect-iq/i/bug-reports/garmin-connect-mobile-ios-does-not-accept-and-characters-for-an-alphanumeric-app-setting

Garmin Express Mac not accepting UTF8 characters
https://forums.garmin.com/developer/connect-iq/i/bug-reports/garmin-express-mac-does-not-accept-utf8-characters-for-a-string-app-setting

Garmin Express Mac not handling maxLength attribute
https://forums.garmin.com/developer/connect-iq/i/bug-reports/garmin-express-mac-does-not-handle-maxlength-attribute-on-a-string-app-setting

Connect IQ Store Android regression bug
https://forums.garmin.com/developer/connect-iq/i/bug-reports/regression-bug-connect-iq-store-version-2-12-android-characters-don-t-working-anymore