I can't report this in-app, because I don't have email set up on my Kindle Fire.
I had a custom reading plan where I was behind. I used the option that's equivalent to "Adjust plan from today" (I don't remember the exact words, sorry). The Plan adjusted to May 8, 2027!
I've noticed a number of other bugs related to Reading Plans on iOS or Fire. Would you like me to list them here, or in separate threads?