Pluggable Transport fail to start
If Tor 10.0.11 (and possibly earlier versions as well?) is launched from another file manager than 'File Explorer' - e.g. from 'Total Commander' (aka Windows Commander) - it will very often fail to start pluggable transport with a message: Starting failed (missing pluggable transport - [obfs4 IP]). The issue appeared immediately after applying latest windows updates (Feb.08.2021), so it might be a conflict between Windows OS and external file managers, but could also be an issue with loading the pluggable transport. Starting Tor without bridges appears to work (mostly).
the (from log below) [WARN] Pluggable Transport process terminated with status code 0 appears now and then as first entry in logs but seemingly does not affect Tor operation - restarting Tor when encountered might be a safe choice though. This might or might not be of relevance to ticket #33669
example of log:
[WARN] CreateProcessA() failed: The system cannot find the file specified. [WARN] Pluggable Transport process terminated with status code 0 [WARN] Failed to start process: (null) [WARN] Managed proxy at 'TorBrowser\Tor\PluggableTransports\obfs4proxy.exe' failed at launch. ... [WARN] We were supposed to connect to bridge '[obfs4 bridge 1 IP]' using pluggable transport 'obfs4', but we can't find a pluggable transport proxy supporting 'obfs4'. This can happen if you haven't provided a ClientTransportPlugin line, or if your pluggable transport proxy stopped running. [WARN] Problem bootstrapping. Stuck at 0% (starting): Starting. (Can't connect to bridge; PT_MISSING; count 1; recommendation warn; host [host ID] at [obfs4 bridge 1 IP]) [WARN] We were supposed to connect to bridge '[obfs4 bridge 2 IP]'...etc..etc. for all listed bridges