[PsychoTechFreak]

All right, this is what I have observed unfortunately, but probably it helps a bit.
Reproduction Check Frequency := 10000, to investigate the real transport issue without influence of reproduction.
WPs not connected, to keep the observation area small.
Krill population transporter can carry 211
Krill colonizer can carry 202
All planets of the isolated system are colonized.

I do NOT see the "cannot load cargo" message anymore, but the transporters do not leave homeplanet anymore if the colony levels reach 500 obviously:
4 Colonies have got 624 M (which is from 1 colonizer + 2 transporters)
1 Colony has got 835M (1 colonizer + 3 transporters)

I just can see the loaded transporters remaining at the homeplanet. They are "flashing" (I have set animation to ON) at the beginning of each turn, but they don't move anymore.

You are right with the 500M stagnation, oleg. This one is hardcoded, right?