Running Software (issues missing this information will be deleted):

• Addon version: 8.3.1

Have you read the changelog? (please don't waste our time)
Mark if read. Read it

Describe the bug
Installed the newest version of PetTracker (8.3.1). Once installed, noticed that another addon (Kaliel's Tracker; v3.21) no longer displayed/tracked my quests on screen. If I disabled the PetTracker, it seemed to work fine. However when they were both running together, only PetTracker seemed to work, and not the other.
Once I rolled back the update to the previous version of your addon, both seemed to be working once again. Uncertain what the conflict is.

I have exactly the same issue. I have gone back to 8.3.0 and it works again. Obviously some conflict with Kaliel's tracker.

Yup

Kaliel's Tracker actively provides PetTracker support, which is simply out of date. Nothing I can do here.