Post combat lock.

if I remember correct, normally, the attacker should be seeing "Base is locked for your alliance" message at the end of 2 minutes combat timer and should be able to attack again within that 30 seconds of lock time, the defender should be seeing that "Post Combat Lock" message. But in his case, he's seeing that Post Combat Lock message as attacker and he cannot attack till the end of that timer as I understood.

Ok? Well might be me that's thick here, but how will that help with base-locking? it only extends the attack period with an extra 30 sec. I never tried base locking but can't really see how that would help...
And what in that case can I do/not do to avoid getting post-combat lock?
It can't be because I hit 2 bases at once since others get it too.

Yes, you are punishing PvPers way too much in a game that is supposed to be a war game.

And yeah, what difference in levels triggers this post-combat lock nonsense?

let's start by saying that pvp-locking was the biggest problem with the game for a couple years (2016-2018) and made the game nearly unplayable
preventing lockdown was a hard nut to crack and took several iterations
in the first iteration of the patch it was introduced that if you attack somebody 15+ levels higher, you get those extra 30 seconds delay
but that did not fix the problem completely because people found smart ways around it that made things even worse
the final patch that seems to have solved the issue for most intents and purposes - was never spelled out in detail so that it is hard to figure out exactly when the extra 30 seconds happen and also hard to find a way around it
i believe that there are two extra precautions: if you are attacked then you get preferential right to attack back for 30 seconds, and in addition your right to continue attacking is discarded seemingly randomly
this random (or seemingly random) feature is what prevents a reliable lockdown strategy from being designed and solves most problems with lockdown pvping
the extra 30 seconds one gets here and there is a small price to pay for solving a huge problem, imho

Can you provide some more specific feedback on this, via PM if necessary?

Will do. I'll tke a screen shot next time....

Another http://prntscr.com/j3kr3q What's happening?

what do you mean by "what's happening" ? you're playing an EA game, what the heck you're expecting ? LOL