>>Sounds to me like the symptoms of trying to ascertain if windows needs an update - although that should be visible in higher CPU usage of 1 core. The only other throttling could happen to CPU if overheated - if CPU cooler is full of gunk, it might result in cutting back whenever CPU gets hot. Just vacuuming the area is often enough, no need to unscrew a often tightly packed laptop.
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>>I would compare data from resource monitor - on disk the speed reflected for the application trying to start and if many .Net assemblies are virus-checked and/or replaced.
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>>Jot down the times you consider slow and compare with things reflected in system logs if you do not see any MS update/virus check/crypto miner activity in resource monitor on CPU and/or disc.
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>>The only other thing I remember was old discs falling back to PIO, but that should not happen to SATA and/or SSD, as the interface is not applicable AFAIK.
>>But back then, whenever OS "saw" many disc errors, the speedy access was cut back until reboot of fix in registry.
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>Thanks, I will check the Resource Monitor next time it happens. I am using Windows built in virus detection. As a security precaution, just in case it would fail on a specific virus, any recommendation on a small virus check utility I could use to see if it would find something Windows would not be able to?

You could take advantage of the free trial period of various AV products e.g. https://security.symantec.com/

You might also want to run Malwarebytes' Anti-Malware (MBAM). This is a tool designed to detect and remove "grayware": products which may pretend to, or actually have a useful purpose, but which also do malicious things like spy on your web activity, change your browser home page or search engine etc. A lot of grayware is not specifically removed by AV packages because some people might actually want the "useful" thing it supposedly does.