Grav admin panel - errors about "mysqli already loaded"

Every time I access the admin panel (and only the admin panel – no issues on my actual site), the following things happen. Any insight is appreciated…

  1. I get a red error box saying “Fetch failed: Crikey! There was an error…”, with more text below than the box can fit. Site inspection reveals the following:
admin.min.js?0495866071:4   Crikey! There was an error...
[some CSS]
Whoops \ Exception \ ErrorException (E_CORE_WARNING) Module 'mysqli' already loaded
Whoops\Exception\ErrorException thrown with message "Module 'mysqli' already loaded"
#0 Whoops\Exception\ErrorException in Unknown:0
Stack frames (1):
[lots of JS and other stuff]


admin.min.js?0495866071:1   POST http://[site]/admin 500 (Internal Server Error)
  1. I get a log entry saying:
    —[2016-09-27 10:22:15] grav.CRITICAL: Module ‘mysqli’ already loaded - Trace: #0 [site]/vendor/filp/whoops/src/Whoops/Run.php(363): Whoops\Run->handleError(32, ‘Module ‘mysqli’…’, ‘Unknown’, 0) #1 [internal function]: Whoops\Run->handl eShutdown() #2 {main} [] []

That’s a problem with your PHP setup, and would give an error with any PHP script. Grav doesn’t even use mysqli it’s just reporting a problem with the PHP configuration.