High BLER whenever buffering

Hi Experts,

I have a UE log when the UE is using Youtube. Whenever the dl throughput goes above zero (i.e., when the video data is being downloaded), the BLER first goes very high (>70%) and then gradually comes to down to 10%. The CQI is relatively stable since the user is stationary and the in cell center.

In comparison - for a trace of whatsapp video or audio call - there is no such case of BLER shooting to very high values.

My current hypothesis is that the UE loses sync with the NW due to inactivity? If this is true; how to show this?

If the above hypothesis is incorrect; since in RRC connected mode the UE should keep on receiving RS to stay in sync, then what can explain high BLER at every instance of buffering.

Any response is appreciated. Thanks.