I have two 5524P switches & a 5548P. Updated the firmware to 4.1.0.20 on all of them. After reloading, the switches are fine for several hours, but eventually the web GUI becomes unavailable. Set the image back to 4.1.0.5 on one of them & it stays up.
According to PRTG, there's no secure protocol available on 443, but if I restart the switch, the web GUI is available for several hours.
SSH login works fine.