Video of Bug

For some reason, Deployer seems to not want to place items in certain chunk. I tried experimenting in random different chunks and found the same thing: that the deployers would not function as intended, not being able to interact with anything or place anything down. I really could not find a pattern of which chunks Deployers would work in and where it wouldn't.

Playing on a server, if that helps.

I tried using the deployer as well and it didn't seem to work. After reading this I tried using it outside my colony and it worked. On another note: Information regarding the deployer and multiple other blocks seems to be missing from the wiki. It would be nice if the wiki contained the basic information (Even if it is just a timestamped link to the Exploring Create 0.2 Video).

I ran into the same issue playing Engimatica 5 when I have chunks claimed by FTB Chunks. The deployers would not plant trees. I unclaimed the same chunk and the deployers planted trees.

I was also having this issue with FTB Claimed Chunks, but adding the Deployer's fake player as an ally fixed the issue for me. This isn't the only mod that I had to do that with either, for example Modular Routers.

Could these chunks be protected through either vanilla spawn protection or other mods's claiming systems?

After reading your comment about "other mod's claiming systems", it made me remember that MineColonies (the mod I'm playing with) has a chunk protection system against explosions and players building on the claimed chunks. Turned off the protection system in MineColonies config and the deployer seems to be working again. I'll try using the Schematicannon and see if that works in those chunks. Thanks for reminding me about claiming systems, otherwise I probably never would have remembered that I had that option on.

Yes, claiming systems. We all ran into it at some point. However, this is exactly what these claiming systems are meant to do, stop players (including ake players) from interacting with stuff. So keep claiming in mind, but i'd say this works as intended.
Mods that do claiming are Server Utils, FTB Chunks and Minecolonies. There might be more i am unaware of, this is just a desperate attempt to document the mods that cause it for the eventual visitor wondering about this in the future