This sounds like it's possibly related to one of these two bugs which we haven't been able to pinpoint just except that you haven't been getting a notification about it, which could just be a new thing since notifications for news posts randomly stopped working for awhile and then just recently were fixed - https://horsefable.com/bug-report/1185 or https://horsefable.com/bug-report/1011

Maybe try to keep track of the boarding center their boarding at and their rules? To see if it's specific centers or not. 

I am having the same problem with some of my friesdales and Frisians. 

I remember that first link, I almost forgot about it, those horses were boarded at home with me if I am remembering it rightly but they were still getting kicked as I had 0 stalls at home and then all of a sudden I had, say 10 of them and I had 10 horses kicked.

The other one though, I don't think applies to me? I looked at each horse's history and I had rescued them all from the Rescue Center. Though once I either brand them, if applicable, put them into a tab, board them and then either mark their paths for Careers only or Explores only or both Careers/Exploring only, I tend to not ever have the need to go in and do anything to their profiles ever again. Usually a one and done kind of ordeal and the second one seems to happen after doing work on them. These seem to be kicked long after I have rescued them and not messed with them further. 

I'll go ahead and re-board them and note here what stables I have chosen and keep tabs on it. I was able to put them all into the same stables, Midnight Horrors. Rules wise seems to be 14 days of activity, 7 days frozen rule and 1 day only for bad payments. DIY Option of $5 only.

Weird, I just had a whole bunch of horses randomly kicked too. Pretty sure I haven't breached any of the rules. Maybe the host account was downgraded and the boarding centre with it?

Yah I have cheap boarding and it's only filling 5/8 stall I wonder if this is happening to my boarders?

Kail, so you have 8 stalls but only 5 boarders currently?

Yes it's weird because my boarding is like 5 bits and I only have five people out of 8 it's bizarre 

More than likely tied to your training center unfortunately. People whose horses are higher tiers for competitions, say like Universal tier Flat Racing, if your Training Center does NOT have Universal tier unlocked for Flat Racing, then no one that has horses at Universal tier can board with you.

I found this out when my cousin had wanted to board with me, but due to how it's annoyingly set up, she could not always board with me, some of her horses discipline tiers were higher than what I had Training Center wise. You unfortunately need to have everything maxed out on top of all the places the horses can train. So not just the indoor/outdoor arena. You also need the Ractrack and Outdoor Course.

I tried to see if I could get it changed but it was vetoed down during a livestream and I've been bitter about it since. Sure I finally upgraded everything but I hated having to do so JUST so my cousin and others could finally board with me because I found upgrading that to be an extremely low priority, ignoring Flat Racing.

and it still makes zero sense because you aren't required to train your horses were you board them. I would reckon most people don't. If you are subscribed, most players will use their own training centers. Otherwise, people can look and train at any random boarding center, so having that tied to where you board your horse is completely senseless. 

I think what is irritating there is that the cost to upgrade those Training Centers is quite high compared to what you're going to gain back from it.  You have to set to 1bit just to make "something" from it and that is never going to pay back the excessive cost of all of the necessary options (English/Western/Racing/Outdoor plus every single Discipline tier), let alone make any form of worthwhile profit.