Just my two cents.
I just found this solution yesterday and now your talking about it. Its my lucky day, thanks.
In my case I used the artistic/watercolor filter a few weeks ago and then the client wanted me to use it again on another image and I couldn't find it again. I blamed it on my note keeping. Then yesterday I refreshed the filter list and it showed up again.
Any idea of why these filters appear and disappear like this? I'm trying to develop a reliable system for serious work and I get worried when stuff like this happens without understanding why. I don't remember updating from the net other than last night.
Dont get me wrong, I'm happy its back, thank you; I just don't know if its something I did that I should not be doing or is something being done to me or for me that I dont understand or know about. I hate being ignorant.
Is there a best practice guide to when an update should be done or a website I should be watching for updates etc.
I'm using gimp 2.9.? on ubuntu 16.4 and my filter count is 493