I am NOT seeing your described symptom on various (7) Raspberry Pis
running the Linux AX.25 stack with Winlink, APRS & Chattervox at 1200 & 9600 baud.
My hardware is mainly RPi 4's and sound cards using direwolf.
I do NOT use Linpac or Gnome3
The two kernels I am using from the Raspberry Pi Foundation (raspbian):
Linux test119022321 5.4.79-v7l+ #1373 SMP Mon Nov 23 13:27:40 GMT 2020 armv7l GNU/Linux
Linux pi400 5.10.11-v7l+ #1399 SMP Thu Jan 28 12:09:48 GMT 2021 armv7l GNU/Linux
What TNC device are you using?
/Basil N7NIX
Basil Gunn