Flight plans electronically filed by Skydemon seem to be 'lost' in the system in Spain.

At AENA airports the ATS reporting office could not locate our flight plans and had to manually create another one.

Then on arriving in France the airport can see two flight plans had been filed.

Is there some technical issue somewhere?

If two plans have reached the tower in France, then the SkyDemon one was certainly successfully sent. The question is, to whom? You should be able to see the addressees on your confirmation email, and it should be a simple matter to ensure that the Spanish facility you were speaking to is able to receive flightplans sent to one of those addresses. If not, please let us know.