I know this error very well. It has started some time this summer and to my mind it has gotten worse over the time. I have written a Reflector thread: SOTA Spotter App: Spotting fails frequently already in September. @YO8SAW and @MM0FMF are aware of this problem, but unfortunately could not fix it.
For the last months about 75% of all my spots fail with the mentioned error message.
My only suggestion: Switch over to SMS-Spotting. My standard procedure meanwhile is: Try to spot via internet connection. If this fails, switch over to SMS-spotting.
73 de Michael, DB7MM