Depending on the timing and sequence of the incorrect calls the device might sometimes recover and sometimes not.
During our testing and firmware development we have surely restared our test devices several thousand times. I have not seen a single occasion where the http interface did not come up correctly. Therefore I do not understand while that happens in your installation on a regular basis.
Currently we are working on a firmware version that will constantly monitor all active TCP connection to make sure there is at least one port that is available. Unused connections will be closed after some time.
You can send us an email to firstname.lastname@example.org
and we can send you that firmware version for testing.