======= I will summarize to clarify:
The issue happened after Calibre 4.10.0 and 4.10.1 in systems with same Windows version. Calibre 4.9.1 and older have no issues
This is not a major issue as no functionality is lost.
1- Its not the windows version: lets rule out the OS version (even if it could be a system issue).
Why? There are users with v. 1909 with and without problems:
With the error: "Calibre-parallel.exe - Fail Fast Exception"
@Horus68 = Win10 Pro v.1709 build 16299 32 bit
@varis1 = win10 pro v.1809
@Iskariot = Windows 10 Pro,
v.1909, build 18363.592
Without problems:
@JSWolf = Win10 v. 1903
@BetterRed = Win10
v.1909 build 18363.657
@DNSB = Win10 v.2004 build 19564.1005
2- @PeterT and @kovidgoyal pointed to Video Driver issues (and Qt WebEngine 5.14)
That could be a good solution. I have an old graphics card (2011... someday a new one will be acquired!) Nvidia GeForce GT 440 (2 monitors setup) with latest drivers (the latest version 391.35 is dated from 2018). I even reinstalled full driver removing the old ones and their settings but the problem still there.
3- I even did a
for my system, also not solving the issue.