Even if that had been the case, because the goblin was lv3 if I recall, so it was *possible* that he had that maneuver (although I didn't see any saving throw roll having been made), another goblin who was only lv1 knocked back another character several meters with an arrow.
Im affraid this was not a bug ...
https://baldursgate3.wiki.fextralife.com/Arrow+of+Roaring+Thunder1. In the goblin camp, you can enter the fortress by breaking the unstable wall, which awakens the sleeping drunk goblins. The first time I went through that part, I fought off those goblins in a few turns, and that was it. The second time however, after the first round, ALL the goblins joined the turn other. What the heck?
Again, possibly not a bug ...
Question here is where was rest of your party, if you are too close to edge and in combat, you need to remember that you stand straight in line of sight of all those goblins down there.

2. So I was in for a tough fight, but I had the high ground, so it was doable. But NOPE, the game had tricks up its sleeves. The bugbear on the high ground dashed and pushed back the cleric more than 5 meters (AGAIN - even if he had already used his action to dash!!!) over the ledge and down a few stories, almost killing her off instantly.
Once again, not a bug ...
Push costs, as far as i know, bonus action.
(Note that i dont comment what it "should cost according to 5e" ... but just what it costs right now, right in this game.)
3. I managed to have her dash away up a platform where she would have some cover and crowd control, but NOPE, a bugbear that was too far to make it to the ladder and climb simply jumped up 4 times his height. Even a bullywug, who can jump 10 feet vertically, would not have been able to make that jump.
Here im affraid we dont have enough information to say anything about it ... but concidering rest of the post, i presume you simply guessed the height wrong. :-/
Screenshot would be helpfull in the future.

4. So I'm down one party member right off the bat for BS reasons, AGAIN. Yet this time, I don't give up, I figure that with the high ground, I can kill the goblins as they try to climb up. But NOPE, they simply run right against a wall at the bottom floor, and voilà! they get teleported to my level instantly, coming out of the rock wall. WHAT THE HECK?!
Again, not a bug ...
This is called "goblin hole", and it was mentioned in Patch 5 notes ... specificly:
* Added holes for goblins to navigate the several levels of the Goblin Camp more easily.You can probably imagine it as corridors dug by goblins as a shortcut.

5. Finally, as a bug made it that combat was frozen after an enemy's turn, I clicked on one of my character's icon to try and unbug combat, and the turn order skipped two of my party members to get to the turn of the character I clicked on.
This actualy sounds like bug.
