Verifying integrity of game cache yields no improvements.

try deleting all the files from these locations:

C:\Users\<USERNAME>\AppData\Local\Arma 3\MPMissionsCache
C:\Users\<USERNAME>\AppData\Local\Arma 3\players
C:\Users\<USERNAME>\AppData\Local\Arma 3\squads
C:\Program Files (x86)\Steam\steamapps\common\Arma 3\Missions
C:\Program Files (x86)\Steam\steamapps\common\Arma 3\MPMissions
C:\Users\<USERNAME>\Documents\Arma 3\missions
C:\Users\<USERNAME>\Documents\Arma 3\mpmissions
C:\Users\<USERNAME>\Documents\Arma 3\Saved\missions
C:\Users\<USERNAME>\Documents\Arma 3\Saved\mpmissions
C:\Users\<USERNAME>\Documents\Arma 3\Saved\steam
C:\Users\<USERNAME>\Documents\Arma 3\Saved\steamMPMission
C:\Users\<USERNAME>\Documents\Arma 3\UserSaved\missions
C:\Users\<USERNAME>\Documents\Arma 3\UserSaved\mpmissions

Make sure to back up all the files with the file types ".3den.Arma3Profile", ".Arma3Profile", and ".vars.Arma3Profile" in these locations before removing them:
C:\Users\<USERNAME>\Documents\Arma 3
C:\Users\<USERNAME>\Documents\Arma 3 - Other Profiles

Try starting your game with no files in any of these places. If you want to back up all these places first then that's fine too.

Deleted all and the problem was solved. What is the cause of this bug?

Thanks so much!

The support of this game is what keeps it alive. Just over 500 hours played and I'm still learning new things about the game and experiencing so much. Thank you for your immediate help and keep up the good work.

Its probably the game thinking you have more memory than you actually have in your pc and attaching it to your a3 profile. Then it tries checking if you do and crashes cause you dont. idk its just what i think