The discrepancy between forecasts by 1h or 3h steps for rain or snow is explained because precipitation amount less than 0.1mm of rain or 0.1cm of snow are not displayed in Meteograms:
https://community.windy.com/topic/15841/1hr-and-3hr-forecast-differ?_=1670949736908
But this is different from the issue mentioned by @sjbuysse concerning waves.

Screenshots right now for Grand Junction. One shows snow and the other doesn't.

I have also noticed this issue with snow. Last night the 1-hour interval forecast said no snow; the 3-hour interval forecast said 0.4 cm; it snowed about that much. The little forecast icons for each hour also did not indicate snow on the 1-hour.

There seems to be a problem with the 1-hour interval forecast. To reproduce, compare precipitation amounts in the next day between the two forecasts. I think it is more noticable when there is a small amount of precipitation, often removing the precipitation entirely in the 1-hour.

It sounds like it happens with waves too.

sorry, I missed you message.
Yes I did.

I actually noticed it again somewhere in the last couple weeks. It's definitely not a one-off.

I'll attach a couple screenshots of that event. The top image is on my browser on the laptop. Screenshots of the same time, taken at the same time, with the same model (AROME)

Again the difference is not small, it's more or less 180 degrees in direction