I have decent PC dedicated for audio production and superb sound interface, RME UFX (newest firmware & drivers). DPC Latency checker shows no peaks. System is on SSD and for audio there are three 2-3 TB drives. OS is Win7 Ultimate.
 
I have recorded bands in multitrack for 5 years with this setup. This year I have seen a new, bad behavior occuring every now and then: recorded audio is not perfect. Maybe once in 5-10 hours of recording a chunk of audio is missing from audio files. Lenght of the missing piece is typically a few milliseconds but it may be even 300 ms. There is no indication of dropout and missing audio can be detected only when playing back the recorded take. It's like the recording has paused for a very short time.
 
The same occurs with the newest Cakewalk as well with the last SONAR SPLAT.
 
Other programs running on background are
- Google Backup and sync
- Adobe Creative Cloud
- Fractal Audio AXE FX II USB driver
- Axe Edit
 
I've tried already to disable them but with no success.  I have not installed any new programs for a very long time that might run on background.
 
Any ideas how to get the recording work perfectly again? How to detect if this is DAW, OS or hardware issue?
 
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Win7 Ultimate
i7
32 GB
Nvidia
RME UFX
Axe FX II
 

I would suspect the Google program.  Back in the Win 7 days (I'm on Win 10 now) I installed Google Chrome.  I started having random dropouts on Sonar.  I uninstalled Google Chrome but the problem persisted. Turned out to the Google updater that was installed when Chrome was installed.  Uninstalling the Updater (which was a mess and a long story) fixed the problem. 
 
Have those programs you list running (but not Sonar) and run the free Resplendence Latency Mon and see if it shows any issues.  I suspect it will.  
http://www.resplendence.com/latencymon
 

Hi. When recording, I would shut down anything that does automatic stuff in the background.
Perhaps even disconnect from the net and shut down AV?
All the best.
Edit: Didn't see who posted at 1st, so this might have been obvious.

given that bandlab are pushing chrome, i reckon they'll sort this out

OK, next I will try to disable network.
 
There is also a tiny possibility that my upgraded Nvidia Geforce graphics card is causing this because it's the only change in hardware I have done for a long time.
 
Another scenario: Could some effect inserted into the project cause this? => Could disabling all FX during recording make any difference.  [to be tested]
 
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More specs: RME UFX in ASIO mode, buffer 256 bytes, 44100, 64 bit engine on, 32 bit recording. RME properties panel shows that everything is OK.