The Map maximum zoom in the plugin zp_openstreetmap is 18?

I set the value to 18 a few days ago. Today I put him at 22. Then I forgot and suddenly there were only gray tiles. Now I needed a lot of time until I found the mistake.

What are you asking exactly? With gray titles you mean tiles? It might happen that map tiles are not available sometimes due to less server capacity (depends on what tiles you use).

Info: https://github.com/Leaflet/Leaflet/issues/5289

Note that the plugin is not yet on the latest leafletjs. Not sure what we should do now, we can add a note or internally change values if exceeding.

The easiest way is probably in the plugin admin page at the option in the description add: maximum zoom level "18".