The public server occasionally becomes overloaded. It is the same public server that is used by Python Gekko for solving optimization problems. Python Gekko is downloaded over 200,000 times per month and also has a local option with remote=False where a public server isn't needed. If the public server availability isn't high enough for your needs, please consider switching to Gekko. There are tutorials at
https://apmonitor.com/do in APM Matlab and Python Gekko. Both use the same underlying APMonitor software. One easy way to migrate is to use the custom trained Generative AI to help with the transition:
https://gekko.readthedocs.io/en/latest/support.html