User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Firefox/68.0

Steps to reproduce:

Recently "Reset" my PC while keeping my personal files. Windows 10 64 bit. After the process was finished and I got Firefox running again. Put the settings back as they were to delete my history on closing Firefox.

Actual results:

History isn't deleting whatsoever. No matter on exiting Firefox or going into the settings to clear it manually nothing happens.

Expected results:

My history should be getting deleted either on closing Firefox or when going into the settings and doing it manually.

It looks like something is interrupting sanitization before it goes through all the steps, maybe awaiting forever.
We should really add more logging to debug these cases, we have a few log calls, but not enough, how do we find where the system is blocked, without a crash report (that at least has progression)?

When you say history, do you mean browsing history?
Could you please go to about:support and run Places Database Integrity there? Does it report back any errors once done?