This has been reported.
Issue is MiG-21 model numbers need to be typed with exace number of digits that skin is designed for. For example if skin needs 3 digits and user enters 1 only the holes will show.
So type in mission editor right number of digits untill this is fixed.
For bort number 3 type 003 etc.
I noticed this also, happens when scrolling to the side. However I have checked it if it happens in the Testers version and it doesn't so, now I am not sure if I should report it or not.
EDIT: Reported
For me I don't have this, I see pilot figure and cockpit in the mirror
There is however clipping issue (but this is not your issue, which as per my screenshot, I don't have) which is already reported
Su-25T airbrakes are not overly effective so there is good chance this is not a bug. Please test deceleration with airbrakes extended and not... is there distinct difference?
There is bug report already for missile sound in external while missile is supersonic (doesn't happen once subsonic), Bug #29091 (http://bagi.eagle.ru/view.php?id=29091)
I think the Jetseat would be more accurate as you have more than one shaker, so you get positional shake (left/right) and buttkicker is mono mode only (unless you have 2 amps & shakers, one for each channel :))