Ok. The logs don't say anything useful at all. It's just the same few lines repeated over and over. I've added it at the bottom of this post. Amusingly '.txt' files are not allowed on the forums here. Only pictures. So I can't attach the text file of the logs.
While doing this, I discovered something really strange. If I go through the following process I get a different error:
Click Vault Settings and choose 'Connect'
Select Nextcloud
Paste in my nextcloud server
https://SERVER/remote.php/dav/files/USERNAME/
Enable 'Bypass SSL Certificate verification'
Click 'Connect'
At this point, I normally get redirected to my web browser where I authorise the connection. But when I enable 'bypass verification' I don't go to the web browser. The program immediately displays a red error Could not connect to specified WebDAV folder. Check your username and password. My web browser never gets activated.
That's weird. Nothing different is in the logs. It's still just the enable/disable proxy stuff.
You ask about VPN and anti-virus. I do use VPN sometimes, but these behaviours are consistent on and off the VPN. My company installs a lot of different security packages on this laptop, and I'm not sure exactly which ones they are. Crowdstrike Falcon is the only one I'm sure about. There's no well-known, heavyweight antivirus like McAfee, Symantec, or Kaspersky.
Here's the logs, for what they're worth.
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Enabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection
Info: [HTTP] Disabling VERIFY SSL PEER/HOST
Info: [HTTP] Using AUTO Proxy detection