Oh dear. Poor Flexi. As you know I had that badly with Minnie a couple of times now.My apologies for jumping on on my problem again with flexi but her crop isn't emptying.
I just found this old thread if anyone is around would you please look and give me any input you may have please.
There is a remedy mentioned and I'm thinking of trying this. I've tried oil and that hasn't worked.
https://www.backyardchickens.com/threads/crop-that-wont-empty.1231683/page-2
I did very frequent massage with lots of coconut oil and last time I added cellulase. It also went sour the second time so I had to treat with anti-fungal. It took almost a week but eventually cleared.
I looked at the thread you posted - it shows a guy turning the chicken upside down. I must say in the video it looks sort of satisfying but I would be terrified if the chicken aspirating so there is no way I would try that!