Last night I was shooting with my Sony a7r3 and an intervalometer I have used many times successfully. ControlMyCamera was set so that 4 seconds was the maximum shutter speed. The interval was 7 seconds. I had ISO set at 100.

Everything worked perfectly -- until the camera shutter speed reached 4 seconds. Then it went to 5 seconds, then 6 and so on. The ISO never changed from ISO 100. This is the first time this has happened to me.

Any ideas? Did I do something wrong?

Thanks in advance.

As you say, normally that works. Try confirming the values for Max and Min ISO once (even if they are set correctly).
Also I'd recommend to do some tests at home by dimming the light with window binds etc. before going out for an important shooting.

Thank you very much. I am going to troubleshoot along those lines, and do some tests. I will report back so you have the information. Thanks again!

it happen to me that the iso doesn't autoramping. I tried to disable NTC function and then works. i will try again tonight and confirm it.