Sudden power loss denies the OS (and services running) the opportunity to shut-down gracefully/cleanly so my uneducated guess is that some kind of session/state data is not cleared and it's presence during boot results in something like ConnMan not seeing that a new connection is required; as it believes one already exists or something of that nature.
The way to investigate that kind of wild-ass theory s starting ConnMan in debug mode (add 'debugging' to boot params in cmdline.txt) and with persistent logging enabled from the settings add-on, as ConnMan debug output is quite verbose and the default system log size will result in log rotation before you've had a chance to login and look.
ConnMan logs are somewhat human readable .. look for errors. Feel free to pastebin them somewhere (don't upload here please).