modem event logs only show the events when i did reset and nothing else.
Here is the screenshot of signal strengths
Comcast technician came and this time seems like someone logical and reasonable. He took some time to test inside and outside of the house with his modem to collect more stats. He observed some quick variations and errors at the start as soon as when modem was connected. Found that coax had bad connectors both inside and outside. I took some pics and will post later. He replaced both of those, and retested everything. No more sudden jumps in reading and no more errors. I will wait for sometime (few days) to see if I need to reset again or the problem is solved now. fingers crossed
Thanks Mark from Comcast.