Due to the limitation of Clusterio, that the Put- / Get-Chest can only be set within the spawn, we found out after testing that within the Factorissimo2 buildings, these can also be placed outside.

Now we have built a few buildings and are now facing the following problem when placing a get-chest (clusterio) within a building, which may also be inside the spawn:

Attempted placing entity outside the allowed area (placed at x 488.5 y -23.5 out of allowed 200)

My guess is (I do not understand the code) that the factory building or the mod is a world of its own, and therefore its own spawn. After a few buildings, the building area of this own world seems to be out of the spawn.

Can the problem be solved somehow?

Yes, Factorissimo2 uses separate dimensions for its factory interiors. For the first 100 factories, Factorissimo2 places each new factory building interior centered at the origin of its own new surface. After that, however, it starts reusing surfaces evenly, placing new factory buildings in a 512-by-512 wide grid in the old factory building. If you check the map while standing in one of the factory buildings where Clusterio doesn't work, you should see another factory building interior to the left of the building you're standing in.

If you want to continue circumventing the Clusterio limitation, you could try and find the first 100 factory buildings you placed and use those exclusively for Clusterio transport, but since you don't like the limitation anyway, I recommend that you simply disable the limitation entirely instead of abusing Factorissimo: Open the Clusterio config panel (any server admin has access to this panel in his GUI) and set the "Chest/fluid bounding box" slider to 0 (this disables the spawn-only limitation completely, so you can place Clusterio chests everywhere on the map). Have fun!

It's that simple, ok.
I did not know that you can disable that and I did not find anything. Thanks for that!
Sometimes you should open your eyes wide :)