Home to Office VPN connection issues

My office has a Dell Sonicwall TZ600 with which I have set up a VPN access point for outside contractors to be able to access the network and upload/download files. Our work environment is 99% Mac, so I have set it up as L2TP, since macs can run that with the stock OS network preferences and no client is needed for the computers, as would be the case with SSL VPN, etc. Yes, it's less secure and all that, but we don't really deal much with sensitive information. Just need to get files back and forth on to the server easier than ftp, or transfer services, etc.

I routinely screenshare to a computer in the office through the vpn from home using the vnc protocol built in to the mac. In the last 3-4 days or so, I can screenshare for about a minute or two, then the screenshare app loses it's connection. Then about 30 seconds later, I will be booted from the vpn with a message about the PPP server not responding. Then if I reconnect to the vpn, I can't seem to screenshare, it basically just has a window that is displaying that it is trying to connect to the IP address I typed in. I could connect via afp (or smb...) but the vnc screenshare won't work. I have to disconnect and reconnect to the vpn sometimes 3 or 4 times before the screenshare will work again. This is affecting other people on the vpn as well.

I don't have a formal education in IT or anything, I am just a dude who is pretty smart with computers and built my own computer for the first time when I was 12. I sort of just became the de facto computer/IT guy at my work. I can follow directions with coding and all that and can navigate around, but I am not really savvy on trying to find the exact point where a problem might be occurring.

Does anyone know of what to look for? Is this something in the Sonicwall settings? I imagine it is. But I can't find anything in there about PPP server or anything like that. And google searches for this haven't been very insightful either. If anyone has some kind of insight that could help, it is greatly appreciated.