Mobs with the MinerAI can bust through walls, and so their pathing AI is neither noticeably bad nor needing of too much improvement. But the pathing of mobs that do not have MinerAI leads to mobs getting stuck near walls that are sufficiently long/wide. Even when a separate mob with MinerAI digs a hole into the wall, if the mobs without the MinerAI are too far from the hole then they will not path to it. They will instead just mindlessly moonwalk at the wall trying to get to the player.

Perhaps the MinerAI should track where mobs dig into walls, and then transmit those locations to other mobs in the invasion so non MinerAI mobs can get through the walls? As it is now, all mobs are essentially required to have MinerAI or get stuck on the walls.

Personally I'd prefer No. 2

I've noticed this as well.

Possible Mitigations

1. Waves include at least 1 miner to clear the path for them.

+ low effort
+ probably will work
- crude
- demands a miner in every wave

2. Improved AI pathing

Enhance AI of regular invasion mobs so they take advantage of carved minepaths
+ lot cleaner
- more involved
- more comp. resources as waves are given larger path seeking
- will still get stuck if they can't get to the mine

3. promote highest elevation spawning

change the spawning location algorithm to promote putting the wave on overland, so they don't have to dig 'up'
+ more natural wave presence
+ less ant-colony
- doesn't exactly solve the problem
- change of spawn algorithm (some math involved) 

while 3 doesnt solve the problem, it's simply just blocking spawns when the mob can't see the sky. And the algo will find another place to put the mob.

2 would be interesting, isnt it sorta like ants where they follow the pheremones left by the other ants?
the miners could leave the "trail".

but there's still no guarantee that the regulars can get to the miner. I think the 'normies' to manage, they'll still need a way to get out- or we need to rethink a bit on how the invasion can be defeated.

Minecraft may just not be kind to the concept of things that need to be 100% cleared, if they can arbitrarily spawn.

doesnt the mod highlight entities of the invasion though, which would show you where they are and if theyre stuck? so then you can get over there and slay em?

it does not highlight them normally. stuck mobs are supposed to teleport after a bit of having no valid paths but clearly this feature is turned down too low by default or not functioning