when I try to unblock a blocked number, the message app crashes or nothing happens.
I have restarted the phone, deleted the contact and recreated it. There is no changes.
Have you tried deleting cache and/or data of the Messages-app?
(Deleting data will most likely delete all SMS-messages, a backup might be required in case you like to save the messages)
Blocked numbers are handled by a separate app com.android.providers.blocknumber found in
Settings > Apps > Show all … apps > top right 3 dot menu > Show system > Blocked Numbers Storage.
You might delete cache (or storage) here.
Both the Settings of Dialer app and Messages contain reference to Blocked numbers, is there a mismatch of your “blocked users” there, or else any complex setting with in Messages > top left 3 bar menu > Blocking > Blocking Manager ??
Are you aware of the list of blocked numbers in Dialer app > Settings > Blocked numbers ?
While exploring Messages > top left 3 bar menu you could confirm if backup and restore of messages is available for your device / build and take a backup if available.
On the subject of backup, always wise to have a backup of Contacts.
Contacts app > top left 3 bar menu > Settings > Export …
Export to .vcf file is convenient and can be stored on SD card and preferably off the device.
In fact, message app has a different blocked numbers list than dialer app.
I clean the cache of “blocked numbers app” → no changes.
I didn’t cleared data because I don’t know which app blocklist is going to be cleared (message or dialer).
Dialer has a lot more blocked numbers (from spam calls) and I don’t want to loose it.
It’s in the blocking manager (message app) the error occurs. Each “blocked number” line has a clickable/touchable cross to revert the “blocked number” to authorized. The error is when I click the cross for the wrongly added number, the message app crashes. So, in my pov, it’s a missing, normally included, functionality (bug).
About backup/restore of all messages in message app, I’m not interested in it because a restore won’t clear only the wrongly blocked number and probably any number because as you said, the blocked numbers are strored in the blocked numbers storage app.