Unfortunately the workaround is not stable.
It works for several times until it crashes again. Flight-mode on/off does only help for a certain amount of time it is no solution for long.

Great! Works on iPhone 6s and iPad Mini2, too! Thanks.

Thank you for the link, but it seems to be problematic, it runs into an error. Have tried several times (on Mac Book Pro, Sierra)

where to report the problem?

... Opera coast worked under iOS 10.2.1 for severals days until the crash(es) occurred.

.. how to make Opera Coast work on the subject?

As it happened nearly simultaneously on both devices there must be an overall reason that lies in something that comes from outside. I tried to reset network setting without result. Does anyone have an idea what else that might be?

From one day to the other opera coast crashes on iPhone 6s and iPad Mini2 both running under iOS 10.2.1.
Neither restart nor reinstallation helps.