Dave,
Looking at the last couple of lines in the error message It seems that the server is trying to write to a log file and failing. As far as I know the server should not be logging anything.
Did you use Ray’s pre-configured image file for the installation? The latest version of the program on GitHub includes a beta of a new UI but it is too early to use that for regular operation.
If you installed the software from GitHub were you using the most recent rev of Raspbian as the operating system? something may have changed there.
I would suggest setting it up for auto start at boot and see if that changes anything. It is interesting that the problem occurs overnight.
I haven’t seen this before.
Dan