Hello,
I don’t think your problem is the same as that encountered by other users since normally a restart of the router would allow it to return to its normal speed for about 1 hour then it would be limited to 220 Mbits,
but you never know, The firmware “12A08” does not have any bug fixes,
it is only the most recent version such as RG501QEUAAR12A09M4G_04.200.04. 200 or RG501QEUAAR12A10M4G_04.200.04.200 which has the bug fix,
but I don’t know if I have the right to give you the download link to the firmware RG501QEUAAR12A10M4G_04.200.04.200 since it is not an official Teltonika firmware,
you can find this topic here
Best regards,