if you can extract a logcat from the time window (a few seconds) when the device sees the decline it’s a hint to what’s happening: [HOWTO] log app errors with LogFox on-device to create bugreports
You can also show it to the publisher of the app.
(on at tangent: Threema Messenger can block anyone that isn’t in the system contacts, something the other mainstream messengers do not offer. Gives some assurance for families / kids)