Today was my FP day. Hopped online and logged in 10 minutes until FP opened. Refreshed at 1-minute and it opened up the ability to make FP. Well, MDE in my browser (Chrome) decided that my family was no longer linked to me. Opened it up in MS Edge - same thing. Opened the app, and it let me make an FP.
I spent the next 45 minutes fighting the app and two browsers. Sometimes it would say that all Fastpasses were gone for all parks on a given day (including freaking November 16 - which is 66 days away). Sometimes my family would disappear (while there are times this seems like it might be nice, FP day is NOT one of them). Sometimes it would say that the FPs I made for a party of 5 were only made for 1. I think I made a grand total of 2 FP through browsers - one each on Chrome and Edge. Every other time there would be an error at some point.
At the end of the day, I got nearly everything I wanted in generally the timeframe I wanted them, but the frustrations of the software were incredible. Hey Disney - instead of pushing an update that lets me shop through MDE, why don't you focus on making it work correctly for ADRs and FP?
So the reason I responded to your post is that I had similar issues with my family not showing as linked through 2 browsers and the app, but then they would come back. For the app, when it happened, I would close out completely then re-open. For the browsers, I would just refresh until they came back. Happy hunting!
ETA: I just went back to the site, and there is this at the top:
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