Comcast blocking modem to modem requests?

I'm not sure if the subject is the right wording, but I don't know how else to describe this.

So, I own a technology business, where I install managed routers, access points, and a variety of other equipment. Up until now, I have never had a problem.

I have a controller hosted on my Comcast Business modem at the office that my clients can login to and check the status of their equipment and make changes if necessary. Basically, I program the router, ap, or whatever to point to a website that resolves to my public IP address. Yesterday, I had to install a router for a client, and I could not get the new router to connect to the controller. After some troubleshooting, I found that the clients public IP (which is also a Comcast business account) is within the same range as our public IP. For example, client's IP (not actual IP) 52.54.56.58 and our IP 52.54.56.59. From what I can gather, Comcast is blocking connections when the modems are within the same subnet, which is why I was not able to connect the client's router to our controller.

I have also had another instance where the security cameras, which we installed at a client's home, was not able to be viewed while they were at work. I had just chalked this up to being a firewall rule that their company had in place that would not allow the specific port to go through. It's not that often that this happens to us, but when it does, it creates more work because we then need to create a custom file for that specific client (however this file can only be created at our office. so this means that we have to then go back to the office--create the file--then go back to the clients location).

Has anyone else ever had this issue, or know how to resolve it.

Any help is greatly appreciated.