So the old server and the new one have different host names? I’d probably stick with that. It can’t matter much if the 301s are slow on the old server since only 301 are going there.
If no one from team chimes in, the next thing you could do would be to try to add don’t debugging to core to see exactly what it’s looking for. It’s conceivable that it is a bug, as Arabic may not be tested and rtl could play in some way. (That’s all speculation.) Maybe try a 3 character slug backward?