Nighthawk M6 on ATT runs great for about 2 hours

I have been running an ATT M6 for about 5 months and it has to be restarted every few hours to maintain speed. When it first connects it runs great… 80-100 download speed. After a little time it slows and then eventually won’t load anything. Still shows full 5G connectivity.

I also had a neighbor have the same issues with one and he was as able to return it to att and is continuing to use his Nighthawk M1 and says it never slows down.

Please help.