When I try to use the basic loader (chute) to insert materials into machines from Pyanodon's Coal Processing, it says, "Waiting for space in destination", and inserts no items, even when the destination is empty. It unloads without issue.

Admittedly I'm not sure which of the two mods might be the culprit here. Thanks!

Miniloaders behave like inserters, meaning they won’t fill a machine if its output slot is full. Could that be your problem?

I'm having a similar issue, but only when I try to manually rotate the loader into Pyanodon warehouses. See below for error code that crashes the game.

The mod Miniloader caused a non-recoverable error.
Please report this error to the mod author.

Error while running event miniloader::on_player_rotated_entity (ID 19)
miniloader/control.lua:174: attempt to index local 'miniloader' (a nil value)
stack traceback:
miniloader/control.lua:174: in function 'handler'
miniloader/lualib/event.lua:15: in function <miniloader/lualib/event.lua:13>

Some mod you have has broken your miniloaders. This error message means that the inserters are still present, but the belt is somehow missing. Could you upload the save game and post a link?