Switch to Google's Messaging app & the issue will be resolved.
Doesn't look like Samsung has plans to fix Samsung's Messaging any time soon.
And as for "unauthorised update", you know that you can turn Off auto updates, both in the Galaxy Store & the Play Store.
You don't have to do anything if you switch to Google's Messaging app, all your contacts information will be there, automatically.
Hi, We suggest you to try factory reset and check if it fixes the issue. Important : Please make a backup and save all information you need before factory reset, otherwise your personal information may not be recovered. Here are the steps to backup your data: Backup from Samsung account--Apps >> Settings >> Cloud >> Backup >> Select the data >> Back up now. Backup from Google account--Apps >> Settings >> Backup and reset. Here are the steps for factory reset, settings >> General management >>Reset >> Factory data reset >> Scroll down to the bottom and tap on Reset >> Delete All.
Well, there's a few other things that you can try.
Boot into Recovery & Wipe Cache.
Boot into Safe Mode & see if the issue persists, if not then it's likely to be a 3rd party app that is responsible.
You mentioned Bluetooth seems to be involved, you could reset your network settings & see if that fixes the issue?
Samsung's Moderators are certainly not technical experts by any means, think of them as tier one support at a call centre.
Many of the Members here are actually far more knowledgeable than the Moderators, who usually cut 'n paste their answers.
But, who knows, maybe a Factory Reset is ultimately what you might have to do?