Heya, 

My 2 tier 3 pets that were 'out' have completely disappeared from my pet list, they're not 'checked in' and basically just all gone. 

Help? I restarted the game on a different server and they're still gone. Thanks. 

When you restarted the game did you check your pet menu to see if they were checked in? I had something similar happen to me but it was all my pets and switching servers fixed it for me. Also did you happen to check all your pets in prior to restarting the game? If you did then like I asked before check your pet menu again after logging back in again. Also if it was during a character change try switching back to the character before you swapped and the pets disappeared and see if that also fixes it. 

If nothing works you will have to send in a ticket to customer support.