I say its a bug.

I think it's likely a bug. 

i don't think this is about whether it's a bug or not, this is a well known bug that comes and goes for a long time now. to answer your question, if you're still getting the horses were kicked message then i think it's worth adding a comment to your original bug report. it sounds more or less like the same issue (horses getting kicked for no reason) with a slightly different result.

edit: to clarify, are the horses being kicked actually ones over their boarding time?

I believe with her previous bug it was horses in her own barn being kicked. This is horses in other barns being kicked and instead of being in transport somehow end up boarded at home when she doesnt have stalls available at home. Im not sure that qualifies as the same bug if so

@forgottenland, Maki is correct. Those horses I had were boarded at home with me and not a single horse was outside to other boarding centers.

To answer your edit, it more than likely comes from I was inactive for a few days. I froze all my tabs at first THEN I froze my whole account. I do recall seeing some boarding centers have as one of their rules you must be active an X amount of days. None of the horses were 0% health or shouldn't have been near that.

https://horsefable.com/boarding-center/reddrookk <-- I have been putting some of my horses in rooks' boarding center and as you can see you have to be active for more than one day, have horses not frozen for a day and be able to afford the center for more than one day. Well, that is how I have always interepreted those guidelines for boarding wtih someone. I was last active Saturday as I saw the new News Post and commented on it post Derby race.

Editing to add: I have 322 stalls for my horses but I have 511, so 189 should be boarded at centers but not all are. I just bought some horses before I took my break and I remembered boarding them out but somehow they are at home when they shouldn't be.

oh i see, i had difficulty reading the original post sorry. that does sound like a completely different bug then.

i feel like the rules work a bit differently though, at least the player activity and freeze rules? mine are both set to 30 days (i know it's weird lol) so if a player has gone 30 days without logging in i can kick their horses, and if their horses have been frozen for 30 days i can also kick them. because otherwise i would be able to kick horses as soon they're frozen, and people wouldn't be able to board with me unless they stay active for a month straight, which isn't the case.

Im not sure whether kick rulws even matter. when a horse is kicked they should end up in transport and not end up boarded at home, especially when you dont have the open space for them

that's true, i had meant to say it was a bit of a tangent but forgot to.
part of me wonders if it could be having both the horses and your account frozen at the same time, i've never done that while boarding at someone's else place but i wonder if that could've confused the game somehow? i don't really see why that would happen though.

Perhaps? I have done all tabs and account in the past but do not remember full details unfortunately and it is strange that they are boarded at home but I legit have no room for them. I DO plan on doing an upgrade, just taking a time is all.