We have seen this issue with workflows involving web-based applications such as the Add-On Manager, App Designer, Live Editor or Simulink Diagnostic Viewer.
The underlying reason is likely because of a proxy setting in the VPN. You can try the following steps to troubleshoot this further:
1) Disable proxy setting in MATLAB:
- Navigate to Home > Preferences > Web.
- Uncheck "Use a proxy server to connect to the internet".
- Check whether this resolves the issue.
2) If you are connected to a VPN, try disabling it to see if it resolves the issue.
3) If you are seeing this error when attempting to open the Simulink Diagnostic Viewer, please try upgrading to MATLAB R2019b or later.