Please be advised that if users are reporting weird rendering / world loading issues with Dynmap 3.1 + Forge 1.12.2 + SpongeForge and they have multiple overworlds; the SpongePowered team fixed a bug that affected how Dynmap loads its world pending render tile list.

As long as you use 1.12.2-2838-7.2.4-RC4065 or newer, you will not be affected by this issue.