Blitzwolf SHP-15 inaccurate power reports

I use a Blitzwolf SHP-15 smart plug to monitor whether the TV is switched on or off. This used to work well, but recently (since one or two weeks), the reported power shows a strange fluctuation after the TV is being switched off, see below. The long interval corresponds exactly to 5 minutes i.e. 300s which is the configured read interval and maximum reporting time configured for state/power in the corresponding DDF. It is annoying because it causes the associated binary sensor (home assistant) to change from “on” to “off” to “on” again, triggering various actions (light dimming, jalousie, etc.). It does only happen sometimes acc. to my observation so far.

Any ideas what could be the reason? The DDF sets “default: 0” for “state/power” so that should be fine at least.

Strange. And the TV is really off during that time ? is it a « smart » TV ?