My Aspire TC-885 restarts without warning and without heavy CPU loads

headupeyesopen

From an Internet search, I've noticed that a number of users have posted the same kind of problem within the past few years. 

My issues are infrequent so far, but restarts can occur repeatedly in short order.  I've installed a temperature sensor, but all the readings are within bounds.  Restarts have occurred with heavy use and light use (e. g., one browser with three Websites open).  So far, they've only occurred when I've been working online. 

I bought my Acer Aspire TC-885-ACCFLi5 (TC-885_E) refurbished (changes listed below), but here is some info on the original machine:

I run it primarily with Ubuntu 20.04, but I have Win10 Pro as a dual boot. 

Refurbished with: 
Intel® Core™ i5-8400 Processor, 9M Cache, 2.80 to 4.00 GHz
256 GB SSD
16 GB DIMM DDR4 Synchronous 2666 MHz

I'm happy to supply any information for someone who might have an inkling (other than CPU temps, which seem to be fine) about the cause(s). 

I have over 30 years of PC experience, but PLEASE NOTE that I'm not a power user, developer or programmer. 

Thanks!

headupeyesopen

Several minutes ago, I had one browser with one Website open, and the machine rebooted.  I checked the BIOS during the reboot process, and I downloaded the complete log lists.  First the BIOS screenshot: