Does this happen without the mod loaded?

No.
also, errors like this: No entry 'bin/config.bin/CfgVehicles/ua_saa_mig21_aa.scope'. arent possible with ua_ not being present..

This is something I'll investigate, but in the meantime please double check your mod installation and provide the modlist you're using. I have not been able to recreate this on a dedicated server and have had no issues with the planes locally. Do the MiG-21s throw errors or otherwise not work in-game?

Looks like this error only occurs when its being loaded onto a server, are you also testing it that way?

@CBA_A3;@ace;@ACE_Compats_RHS_Compats;@RHSAFRF;@RHSGREF;@RHSSAF;@RHSUSAF;@3CB_Factions;@ZEN;@ZEN_ACE;@UA;

Is the modlist, that was used to verify that this mod is the issue..
Take this mod away and it doesnt spam the config on the serverr.

Yes, I've placed them on a dedicated server without error. I changed the parent classes for the MiG-21s in this latest update, so let me know if you're still getting errors.

Latest update has changed the errors but they are still there.
Same thing but different parent class.

I presume what you've pasted above is your server's load order, and to my knowledge there is no portion of this mod called "UA" or "@UA". Please check that you've got the mod name correct. Does placing or using the MiGs cause any errors besides the one in the console?

Please provide a full log, if you'd like you can add me to send that over.

@UA is the folder name on the server. this has 0 effect on the mod itself.