Of course right after I asked I spotted an elemental spawner in radar range, went to check and got myself some colored alien artifacts. My usual (lack of) luck.
Everything works fine then. Sorry.

Do aliens require a specific evolution level before they can spawn enemies able to drop colored artifacts?
I tend to slow down alien ability to spawn new bases by a large margin so they simply may not have spawned yet but in my previous playthroughs (few years ago) I was under the impression that ...

I haven't tried tanks in a while though. I wasn't impressed with their mobility challenges in vanilla. What do you normally use when you're about up to early blue science and the evolution factor is at 50%?
I used the tank fitted with explosive cannon shells on my current playthrough: that wasn't ...

That was probably the same issue boro reported here as I've been able to assault few alien bases in 0.15.15 without a single crash.

Since the game has been updated to 0.15.14 Bob's Enemies crash my game.
While I can't be 100% sure that is because of that mod deactivating it I haven't been able to reproduce the issue. And that may very well be unrelated but I think the game crash the moment my tank is hit by a fire projectile ...