Someone in the apple community support page said to try this: Go to Settings > Apps > Calendar > Search, turn off the 2 settings there, reboot your device and turn those settings back on. Wait a few minutes for the search index to rebuild.I followed these steps and initially I didn’t see it was fixed. Tried searching again in 30 minutes and everything (search) works again.
Beide staan wel in het Engels, weet niet of dat hier van invloed is.