Updated tvheadend from 4.0.7 to 4.2.4 not playing recordings

Tvheadend is running on separate HW
Upgraded from 4.0.7 to 4.2.4
Now Tvheadend works over its own web interface. I can watch live and recordings
On XBMC I can watch live, but not recordings. I see this in the tvheadend log:

2018-01-13 11:47:04.802 [WARNING] htsp: [ | Kodi Media Center ]: failed to serialize data

The TVH guys will probably know more about this

Yes. I have asked there. FWIW, 4.3 seems promising. On 4.3 everything works, even FFing, but I cannot schedule new recordings.

Edit. Bug. Got a fix this morning, testing.