Since you mentioned "no mods" and this is most likely a SkyUI issue (Enderal does not modify the inventory menu), I assume you are playing the outdated version on Steam. My only guess is SkyrimCustom.ini from your Skyrim SE interferes and you need to update SkyrimRedirector.dll. See this doc on what should be done for 2.0.12.4.
Quick Google search shows that MCM Helper for a wrong version of SSE may cause this issue. Other than that, no clue.
Quick Google search shows that MCM Helper for a wrong version of SSE may cause this issue. Other than that, no clue.