We have seen this issue with workflows involving web-based applications such as the Add-On Explorer, App Designer, Live Editor or Simulink Diagnostic Viewer.
The underlying reason is likely because of a proxy setting in the VPN. Please try out the following steps:
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) Make sure you firewall/antivirus software does not block MATLAB.
4) Upgrade your MATLAB to R2019b or later.