iPhone hotspot wont let me use VPN

I use a VPN to access certain programs for work. Several months ago I noticed when using my phone hotspot I can no longer access those parts of my work. 

Any ideas why the change or how to get around it? It seems like it happened 5 or so month ago. Just want to work while at my daughters various sports practices. 

The VPN works fine though other WIFI, just the phone hotspot is the issue.