Okay so i have done some testing here.

I am not sure if this is a Vanilla related issue:

The vanilla water Canteen is working, any modded retexture canteen is not working when its empty.

Taking a Vanilla Canteen and filling a modded canteen with water 1% very tiny bit, it will allow you to fill up.

Now onto the crops its the exact same issue, when its dry you cant water it, make it rain for 2sec then use water can it works.

somehow these 2 issues are related.

It isnt just the greenhouses and poly tunnels though, its any dug plot, even the one on the ground. We attempted using vanilla only items each time we tested, but could not get them watered unless we made the server rain, as mentioned.

In T185548#2689473, @HoneyPot wrote:

It isnt just the greenhouses and poly tunnels though, its any dug plot, even the one on the ground. We attempted using vanilla only items each time we tested, but could not get them watered unless we made the server rain, as mentioned.

When it comes to garden plots themselves, we are aware that the issue can occur sometimes and it is being looked into. However in the specific case provided by the reporter on the video, the garden plot was not dug