Error 500 on development site

each time we try to load the home page we find a file "com_jfbconnect" in the cache section

JFBConnect will always cache some data regardless of the cache settings of Joomla. If you really want to disable our cache, go to the JFBConnect -> Configuration area and set the cache duration to '0' or set "Enable Debug Mode" to 'Yes', which will disable cache and show additional error information when problems are encountered.

We have run the autotune, we saved all the default suggestions but still we see a blank home page on the front end.

If you're getting a blank white page, please go to the Global Configuration area and set Error Reporting to 'maximum'. A blank white page means a PHP error and increasing error reporting should show the actual error on the blank page.

The 500 error in Autotune is because your home page can't be loaded. Once the error is determined and fixed, then Autotune should be able to load your page properly to perform the checks.

I hope that helps,
Alex