I decided to install and update the Protean theme, however after doing so when any of the mixes are selected within the Design menu on the front-end, it results in a 502 bad gateway error message.
This does not happen with any of the other themes that I have active at the moment, nor did it occur when I tested Ocean. Unsure what is causing this theme to fail to change the users site theme.
Hello. You may try to the ways from this thread: