I figured it out. Apparently, it weren’t items like haard_eetkamer_winter_OFF which changed the status of haard_eetkamer_relais_in_werking. That was only done by these items:
Switch haard_salon_IN1 "Haard salon - IN1" <switch> (haard_salon_groep, haard_salon_relais_in_werking) { channel="esphome:device:haard-salon:in1" }
Switch haard_salon_IN2 "Haard salon - IN2" <switch> (haard_salon_groep, haard_salon_relais_in_werking) { channel="esphome:device:haard-salon:in2" }
Switch haard_salon_IN3 "Haard salon - IN3" <switch> (haard_salon_groep, haard_salon_relais_in_werking) { channel="esphome:device:haard-salon:in3" }
… which were linked to this in the ESPHome yaml:
- platform: gpio
pin: GPIO13 #D7
name: IN1
id: IN1
inverted: true
I deleted these items, as documented in the last sentence of this post. I now recreated the items, and all is well again.
Thanks for your help once more, @rlkoshak!