I haven't had the issue for a long time, but I seem to remember,...
if I closed all of my open windows (except for the floor plan) I was then able to save.
Also, as AC17's autosave is pretty robust (I have autosave set to "Ultra Safe" i.e., save each step), I've had good luck force quitting AC and restarting/opening the autosaved PLN.
Works quicker than you can say your name
Marc Corney, Architect
Red Canoe Architecture, P. A.
Mac OS 10.15.7 (Catalina) //// Mac OS 14.5 (Sonoma)
Processor: 3.6 GHz 8-Core Intel Core i9 //// Apple M2 Max
Memory: 48 GB 2667 MHz DDR4 //// 32 GB
Graphics: Radeon Pro 580X 8GB //// 12C CPU, 30C GPU
ArchiCAD 25 (5010 USA Full) //// ArchiCAD 27 (4030 USA Full)