Question Playing a local video lags after about an hour

[steven1227]

A friend has an HP laptop HP Pentium N3510 Model# 15-d038ca
8GB RAM, 750GB disk (5400rpm)
Win10 x64
It came with Win8 and has been upgraded to Win10 for awhile now. When it first updated to Win10, playing videos seemed fine. But after one of the updates (specific one unknown), videos started developing a lag with the audio (I.e. the video becomes out of sync with audio) - usually after about 45-60 minutes.
By "local" video, I mean playing from the C: drive. So we've ruled out streaming issues, NIC, WiFi, USB etc. A re-boot clears the issue and it can play again for another 45-60 minutes before it appears again.
Doesn't matter which media player - Windows Media Player, VLC, etc.
And file type - MP4, MKV, AVI irrelevant
The pagefile is about 12 GB
Tried updating drivers but they all appear to be current.
Also running Avast and Malwarebytes, if that's relevant.
Been a long time PC user and this one has me pulling out what's left of my hair.
Going to run HP diags next.
Update: No issues identified with HP hardware diagnostics
CrystalDiskInfo shows everything ok
sfc /scannow ran fine.

Any suggestions would be most welcome.

 

[rgd1101]

did you check ram/hdd usage when you have that issue?
and the cpu temp?

 

[steven1227]

did you check ram/hdd usage when you have that issue?
and the cpu temp?

Thanks for your questions.

Here's what we were able to track so far while the lag was occurring
CPU temp while lag is evident is 65C
TaskMgr shows
CPU 87%
Disk 48%
Memory 47%