I have gone thru at least 3 issues on this page to search for solutions and so far none of them have worked. But as the title says, storms in MP servers in 1.12.2 do not spawn anymore.

May I suggest giving weather2-remastered a try? A good friend of mine is rewriting this mod for 1.12.2 as it's something he really loves and wants to improve for the future^^

Kind regards,
Fartsy