So if you format your recurrences using the P1D format, taskd will reject them. I renamed all P1D to 1d and the error no longer occurs. This happens in Task.cpp, there's even a comment about it. Just needs to be accounted for. I'm gonna take a whack at fixing this myself, though I'm not super familiar with C++.
[!IMPORTANT]
Taskserver is only compatible with Taskwarrior 2.x, and is no longer actively developed.
See man task-sync for task synchronization with Taskwarrior 3
So if you format your recurrences using the P1D format, taskd will reject them. I renamed all P1D to 1d and the error no longer occurs. This happens in Task.cpp, there's even a comment about it. Just needs to be accounted for. I'm gonna take a whack at fixing this myself, though I'm not super familiar with C++.