I have the same thing on Altium 20! 2 parts right next to each other in the same int lib, sharing the same sch / pcb libs. Pushing 1 part to the pcbdoc no issues, pushing the other part to the pcbdoc throws 'footprint not found!'
Have deleted / re-pasted / renamed pcb footprint object, sch object, recompiled the intlib, etc... trying to fix the library links. Nothing!! The part in my schdoc even shows the correct footprint model, but it can't push to the pcbdoc! Completely crazy...
Edit:
Ok I found the issue but not the root cause. For that particular component that could not push to pcb, I dug into the 'item manager' list from the tools menu in sch editor. That component somehow did not know the library it came from even though i kept deleting it and re-placing from the existing library. The 'update from libraries' link was broken too, even though I had just placed it from that install library. Maybe the project had cached a broken library link from somewhere else? I don't know I never found exactly why it happened. But! There is an option in 'item manager' to select the library / component. Once I did that the links were restored. Very vague, it took me probably 6 hrs total to work this one out, hope it saves somebody some time...