Having the same problem at several customers, they are all up to date at UTM 9.506-2.
One SW version is giving the problem, others on a SW version are without the problem.
One SG115 is giving the problem, others with an SG-115 are without the problem.
The problem only appears in Chrome. The problem also existed in previous versions of UTM (9.4, 9.3, etc.)
Is there any solution?
The same thing has been happening to me, but it is specific to the following:
* Chrome browser on Mac, running macOS 10.12.6 Sierra.
* Only the hardware SG125. I have no issues with a comparable UTM running in a virtual machine. Both are running the latest UTM software.
* It works okay if I use Safari on Mac.
It started out intermittently sometime last summer, perhaps early Fall. It has gotten worse over time, to the point where I cannot connect using Chrome. I cleared out everything from Chrome and restarted the application. I also reset it to factory defaults. Nothing works so far.
Why do I care? Because Safari is my primary browser, and it is set to block popups. I use Chrome for a few websites and features only. That includes websites with pop-ups, such as the live logs from the UTM.