missing data (15.16)

Yesterday I already reported on random reboots whilst viewing the morning report.
forums.garmin.com/.../the-device-is-restarting-15-16

Today it didn't crash, but I'm missing more and more data:
Training readiness and HRV-status said 'no data', despite having the current as well as the past data

I tried:
- forced/unforced reboot
- software reinstall
- sync via Express