[14:43:57] [Client thread/ERROR]: The mod worldprimer is expecting signature @fingerprint@ for source worldprimer-1.12.2-0.6.0-dev.20190108.182306.jar, however there is no signature matching that description
[14:43:57] [Client thread/WARN]: *********************************************************************************************
[14:43:57] [Client thread/WARN]: ***** WARNING *****
[14:43:57] [Client thread/WARN]: ***** *****
[14:43:57] [Client thread/WARN]: ***** The signature of the mod file 'worldprimer-1.12.2-0.6.0-dev.20190108.182306.jar' does not match the expected fingerprint! *****
[14:43:57] [Client thread/WARN]: ***** This might mean that the mod file has been tampered with! *****
[14:43:57] [Client thread/WARN]: ***** If you did not download the mod World Primer directly from Curse/CurseForge, *****
[14:43:57] [Client thread/WARN]: ***** or using one of the well known launchers, and you did not *****
[14:43:57] [Client thread/WARN]: ***** modify the mod file at all yourself, then it's possible, *****
[14:43:57] [Client thread/WARN]: ***** that it may contain malware or other unwanted things! *****
[14:43:57] [Client thread/WARN]: *********************************************************************************************

I recently accidentally removed a local gradle config while cleaning up old gradle caches/files, causing some of the recent mod files not getting signed... I uploaded a new build which is again signed properly.