in macOS mojave apps freezes and beachball appears for some seconds when doing tasks like loading a conversation in Messages macOS 10.14.6 on my MacBook Pro early 2015 13" with an i7 and 16GB Ram the active app freezes for some seconds when doing tasks in it, like loading conversation in Messages (happens not on every conversations, more like.. every fifth or sixth I click), clicking into Address Bar in Safari or calling up the context menu and I can't figure out why this happens. It happens at any time, means right after a restart.
It existed before the 10.14.6 update.
I uninstalled a clipboard manager which I use and thought it could have sth. to do with it... still existing.
I always look and try to figure it out via Activity Monitor, but no clues.
I booted into Safe Mode... still existing.
I reinstalled macOS via Recovery Mode... still existing.
I also tested my RAM with a memtest86 boot stick. Nothing.
My guess is it would still be present when I recover from a backup... are there any other clues or things I can try to figure this out without installing everything from scratch? Help would be much appreciated. Thanks in advance.
This is easy to isolate.

Sign out of Messages and make sure no other app or system is causing the slowdowns. The more you get freezes, the quicker you can know that it’s just messages causing the slowdown as opposed to being impacted. YOu might open Activity Monitor and show all processes to see which are using a lot of CPU.

Then you can make a new user account. In that account - only sign in to messages - see if the slowdown is there (assuming you concluded it was the cause above).

If so - then you might check with Apple Support to be sure you don’t have an issue server side and possibly consider backing up and restoring your Mac to make sure it’s not part of the system that’s stuck or causing the slowdown.

Keep in mind, for physical hard disks - the first sign you get of imminent failure can be slow apps, so maybe make a good backup first and then test to isolate what’s slow.