TIA has never stamped me in and out from multiple trips there. Going from Albania to Kosovo they don't stamp either way. I've been stamped going into Kosovo from North Macedonia or arriving by air. Last year when I went from Montenegro to Bosnia they didn't stamp me in but I managed to ask the bus driver to go back to the post and get a stamp (since everyone stays on the bus and the driver collects all passports). Haven't got a UK stamp since 2018.