It still is happening, this time with more and more users 
I tried downgrading (not to previous version, but to version before 5.2), but still happens. I don’t recall what version I was using before.
Here’s a list of my mods:
├── Aliases-1.0.jar
├── CommandKits-v1.2.0.jar
├── EconomyLite-5.0.0-2.9.0.jar
├── FastAsyncWorldEdit-forge110-17.02.08-07945af-507-10.8.1.jar
├── Gameshark-1.10.2-5.0.0-universal.jar
├── griefprevention-1.10.2-2.3.1.255.jar
├── holograms-2.1.1.jar
├── LuckPerms-Sponge-3.0.9.jar
├── MysteryGift-1.10.2-0.3.1-universal.jar
├── Nucleus-0.25.0-1.10.2-S5.1-plugin.jar
├── NucleusMixins-0.25.1-5.1.jar
├── nuvotifier-universal-2.3.3.jar
├── PayRespects-1.0.2.jar
├── PixelAnnouncer-1.10.2-1.0.1.jar
├── PixelExtras-1.10.2-2.2.4-universal.jar
├── Pixelmon-1.10.2-5.0.1-universal.jar
├── PixelmonEconomyBridge-1.10.2-1.2.2.jar
├── PixelShout-1.10.2-1.1.2-universal.jar
├── seriousvote-3.2-Bleeding-F.jar
├── spongeforge-1.10.2-2221-5.1.0-BETA-2208.jar
├── SpongyChest-1.10.2-0.4.8-universal.jar
├── webapi-1.9-sponge-5.1.0-SNAPSHOT.jar
├── WonderTrade-1.10.2-4.4.5-universal.jar
└── worldedit-forge-mc1.10.2-6.1.4-SNAPSHOT-dist.jar
Seems to be the same error given here: Internal Error - #22 by Gershon