Were your birds vaccinated for Marek's?
I've lost my entire flock in the last 6 months. 75% showed sudden lameness that progressed to curled toes, to paralysis. Most also were accompanied by a sort of crop stasis. Two more so than the rest. I tube fed, bought all kinds of meds to treat all the other things that went wrong, etc.
@casportpony can tell you the time and effort I've put into my birds over the last year.
I sent my closest girl to the state lab. Came back "likely Marek's".
I know you don't want to hear Marek's, but that is immediately what it sounds like. The lameness and the crop issue. I sent my girl off in September. Virus (Covid) was still prevalent. I wore a mask to drop her off. Keep an eye on the rest of your flock. If you experience any more symptoms similar to your first girl - get a state necropsy done.