crashes on exit, invisible objects andpersp camera goes wild

[bhadrabalaramadas]

Hi all!

specs:
Win 7/sp1 all updates
I7 4790 K
gtx 970
32 Gb ram
Maya 2018.6
Maya 2020

All was good until I installed Maya 2020 at least at this point I noticed this really weird issue. Prior to Maya 2020 I had 2018 and 2019 installed. I have several projects with scenes with no issue. Troubles begun when i installed Maya 2020. Upon activation Maya insisted that it requires Internet Explorer 11, which I didn't have installed on my system atm. So I wanted to install it, but now windows 7 persistently insisted that I should also install all of the Win 7 updates, which I did. Then I installed IE11 and was able to successfully  activate Maya 2020. After that I uninstalled Maya 2019.2, Bitfrost, substance and Arnold for that particular version.

Sorry for detailed intro, but I want to be clear from the beggining
Now I have 3 issues.

Issue 1:
Both Mayas 2020 and 2018.6 crashes on exit each time, which was not the case earlier. I googled and tried all solutions I have found with no success.

my steps to solution:
- Installed 2018.6 over 2018.5 which was installed before the problem started
- I checked for KB4040973 a win update which is mentioned here as a possible cause for Maya crash here

but which I don't have on my system
- I also deleted preferences
- Installed new driver for graphic card
- I even gave all permissions to a users to cmd.exe as it is suggested as one of solutions in above link

But unfortunately nothing helped

Issue 2:
In every scene I have in several projects a few random objects from scenes disappeared from viewport but are clearly visible in outliner, some even have history on them.
The ones with the history on them I managed to save and make visible again, by deleting the last action on them.
If I open the same scene with another version of Maya same thing happens and if I open the same scene on another computer everything is completely normal and perfect. my wild guess is that win 7 update somehow causing Maya old scenes to behave strange.

Issue 3:
When I open same scenes as before and LMB click on empty space i perspective view it makes camera moves away form scene. Each click moves camera more and more aside from the scene by random distance, which I observed in channel box. Usually even 1 click is enough that whole scene disappears from the view. For example if my scene has a building of a 100 meters, camera jumps away from it with each click (235m, 650m, 2300m, 6812m or similar).
Now again, if I create new scene and import this "broken" scene in it everything is O.K., except that missing objects are still missing and when I exit both Maya versions crashes or should I say freeze. Simply nothing happens and I am forced to Ctrl+alt+del to kill the process.

I tried everything which crossed my mind, and this is the best I have found, but I have to many scenes to import them all in new documents, and it's also not a real solution, so any help will be greatly appreciated.