Ambula not spawning

[(NSW)Yaibajin]

So I finally got to bothering with farming ambula for their amino beacons and I actually managed 2 runs into hades and got trinity systems and neuro.

But after those two run I noticed an immediate drop in ambula spawns. And that I mean I had 1 ambula that dropped a trolly 4 totalling my current count to 19 when the Minth run usually landed me 2 ambulas dropping me 5 each.

Now no ambulas are spawning. And I just did 20 waves in outer terminus and 30 waves on venus defense. Is DE blueballing me from completing the set so I get frustrated and just buy the frame in the market? Because this is what it feels like.

 

I suspect that there was some arbitrary cool down (at which case, why this but not arena fights on sedna?). But according to the threads I read. Its been a long standing bug and I have not found any explanation on it. Only various hot fixes to exploits and from what I can tell not actual fixes for the subsequent bugs. Still suffering from post plague star syndrome (my god that drone), don't tell me I have to get that hot feeling of despair all over again with a normal part of the game.