When File->Preferences->Sketchbook location is set to a directory which is monitored by dropbox client, installation/upgrade of libraries interfere with dropbox client and do not get renamed to the proper final name of the lib but remain as temporary folder arduino-\d+.
Upon upgrade, this leads to multiple libraries in different directories and the builder not being able to consistently select the most recent version (see also issue https://github.com/arduino/arduino-builder/issues/366).
This issue is discussed on the forum thread https://forum.arduino.cc/index.php?topic=724169.

I tested with ArduinoIDE 1.8.13 on Windows 10 and a recent hourly build 2021年01月24日 ... both showing the same behavior.

Attached a trace with Sysinternals Process Manager: Logfile.zip
Filter settings: ProcessMonitorFilterSettings
I suppose the interesting two lines are the ones with Result equal to SHARING VIOLATION and INVALID DEVICE REQUEST.

I also tested the IDE with directories monitored with the latest versions of nextcloud client and megasync client. Both worked well during fresh installs and up-/downgrades of libraries.
On the other hand, arduino-cli worked well with all three sync clients.