First of all:

-Make sure you have Openiv.asi plugin installed (OpenIV > Tools > ASI Manager)
-Always install OIV files choosing Mods folder
-Make sure you have ScripthookV and Asiloader installed (http://dev-c.com/gtav/scripthookv/)
-Run game launcher as administrator (Rockstar games launcher, Steam, Epic games launcher or whatever .exe you use to run the game)
-Make sure to apply all steps of this guide: https://gtaxscripting.blogspot.com/2019/05/gta-5-added-peds-limit-fix.html

Huge part of issues that users have are due to other mods, to test if this is your case, do the following:

Test with a "clean gta", with game closed: 

-Rename Mods folder to Modsss and Scripts folder to Scriptsss (this will be your backup).
   *When you rename those folders you disable big part of the scripts and modded files
-Verify game files integrity with your game launcher (Steam/Rockstar/Epic) to make sure you didn't modified RPF files outside mods folder
-Install nibshdotnet again to have NIBMods menu (https://www.patreon.com/posts/22783974).
-Install the mod OIV files only (Nothing else: no peds/skins, cars, etc.).
-Open the game and test with "keep player character" suit.

If the issue doesn't happen, it means your problem its related to other mods you have, now its up to you find out which one...