This question is asked so frequently that it would be helpful to have a sticky in the Help/Advice forum. I could write a sufficiently detailed post about how to do it in different operating systems, and, in the event that someone misses that sticky when going to post asking for help, we could just link them to it directly.
You and I seem to be on the ball for these requests specifically xD so I totally agree with this idea. Create it and then go from there!
Here goes nothing! https://royals.ms/forum/threads/how-to-fix-pet-auto-hp-mp-rissas-guide-v-8-7.106083/
There is some glitch that happens where your pet heal does not work. Although a simple PC restart is usually enough for a fix, a clean boot is sometimes needed. (Restarting the client doesn't seem to do anything.)
I don't know if it's the same issue, but what happened to me before is when you get hit 1/1 and your pet has both HP and MP, they don't work together. But I don't think its a glitch, it always been like that in gms.
It might also be worth mentioning that this computer issue usually also causes you to no longer see monster hp and level, and no longer allows you to cast the warrior ability called rush. Both those issues are fixed the same way as the autopot one.
Iv had the monster hp problem before. What worked for me was restarting my computer. I was cold booting(shutting down) my computer for the first few days, but that didn't do anything for me. What actually worked was "restarting". After the restart I was able to see monster hp again.