I dunno, honestly I find that my fasts can vary pretty massively from one to another. I imagine it’s largely psychological, like you mentioned, and I do think it’s important to try not to beat yourself up about breaking a fast. If you feel awful and you’re certain that it’s as a result of the fast, rather than being tired due to i.e. lack of sleep, you could always do shorter fasts and work up to extended ones. I can do ADF reasonably comfortably now but have been fasting on and off for years and have basically done IF/OMAD consistently for like 5-6 years now.
I have had the same issue! I completed a 28 day fast back in September, but lately breaking 48 hours has been impossible!
I really want to do another extended fast but I guess I am putting too much pressure on myself.