Thank you, I have identified the problem, it is with my code.
BACKGROUND INFO:
Because this mod has to use hidden entities to make much of its functionality work, and those hidden entities are not meant to be built by the player, the mod scans blueprints in your inventory to purge those hidden entities. (There's not really much of a better way to deal with this problem, since the game's logic surrounding blueprints is very complex)
Several of your blueprints in inventory are over 20 MB large, and scanning them causes lag spikes.
Putting those blueprints into a chest or the blueprint library removes the lag, since only "finalized" blueprints can be put in those places, and thus the mod doesn't need to scan them.
I will work on optimizing the logic of my mod to improve performance regarding large blueprints, and maybe see if I can come up with a system to only scan relevant blueprints. This might take some time, but I have a day off this weekend I can try to work on it.
WORK AROUND:
In the meanwhile, you can avoid the lag spikes by storing blueprints & blueprint books in your blueprint library. They can still be assigned to hot bar slots.
