Upgraded from 4.0 - prusa clone running a smoothieboard.
Had zero issues printing from USB on 4.0, literally hundreds of prints - 4.1.1 constantly disconnects in the preheating phase.
Log output:
Connected to machine!
SENT: T0
SENT: G90
SENT: M82
SENT: M106 S0
SENT: M140 S55
SENT: M190 S55
READ: ok
READ: ok
READ: ok
READ: ok
READ: ok
READ: B:23.7 /55.0 @255
READ: B:23.7 /55.0 @255
READ: B:23.8 /55.0 @255
READ: B:23.9 /55.0 @255
READ: B:24.1 /55.0 @216
READ: B:24.2 /55.0 @255
READ: B:24.5 /55.0 @233
READ: B:24.7 /55.0 @255
READ: B:25.0 /55.0 @255
READ: B:25.2 /55.0 @255
READ: B:25.5 /55.0 @255
READ: B:25.8 /55.0 @255
READ: B:26.0 /55.0 @255
READ: B:26.3 /55.0 @255
READ: B:26.6 /55.0 @255
READ: B:26.9 /55.0 @255
WARNING: Device unplugged while connected to port
Total build time: 0.96 minutes
Disconnected.