… there is a related BUG here: [persistence] Forecast Items only update whilst future states exist · Issue #4462 · openhab/openhab-core · GitHub
also noticed by @weymann here: Energy Forecast Binding - #30 by weymann
adding @Mherwege who has responded in time series issues before like here: Possible inconsistency on persistence Layer / possible Item State inconcistency · Issue #4662 · openhab/openhab-core · GitHub