No bluetooth connection to SM Tripower


I succesfully installed SBFspot in 2018 and it logged the data from my Sunny Tripower 7000TL-20 using the usual cronjobs. I just realized that it stopped working on 6th Jan 2019 (SBFspot.cfg is unchanged since 2018). When executing

/usr/local/bin/sbfspot.3/SBFspot -v -finq -nocsv

I get

Connecting to 00:80:25:3A:78:0B (10/10)
Sun Feb 24 13:51:34 2019: CRITICAL: bthConnect() returned -1

The bt seems to be up as

sudo hcitool scan

results in

Scanning …
00:80:25:3A:78:0B SMA002d SN: 305076149 SN30507614

Any idea why SBFspot cannot establish the BT connection any more? The system is raspian stretch.