Step 1: Set the gamerule to keepInventory true and gamemode 1
Step 2: Fly Around in your Tardis with the flight panel
Step 3: Land
Step 4: Spawn Bessie in the Tardis
Step 5: Get in Bessie
Step 6: Click on the Tardis Doors
Step 7: Look around for your Tardis. Then try moving around. You may notice that you can't move and that you're in some random location.
Step 8: If you manage to move summon the Tardis with the key
Step 9: try entering the Tardis, you'll keep getting put back some steps very time you try.
Step 10: Do /kill
Step 11: Summon your Tardis again with the key
Step 12: Try entering it
Step 13: You may encounter isssues
Step 14: You will remember Bessie didn't leave the Tardis with you. You will also notice that Bessie did not stay behind in the Tardis.
Swd, please take a look into this issue