Think the render cycle is up to 1km minutely "except" as you observe sea. These and the 2km zoom and further out like nightly. One of the insiders replied to me a while ago on the community forums as the 2km and up used to be weekly on Friday night.... so it's patience till like 04:00 CET also because OSMI only diagnoses in a 24 hour cycle to see if any other breaks need fixing.

When getting conflicts in JOSM, a) I run an update modified and b) usually choose the 'their version', accepting that the other mapper was quicker.

ciao