Is this the loading.gif file you're using - https://forums.gameex.com/forums/topic/26780-using-an-animated-png-file-for-loading/?do=findComment&comment=204255 ?
Using that image i can recreate your issue on my desktop pc - but only if the width of the loading gif file is greater than the screen resolution width, if i reduce the width of the gif to less than the screen width (just using https://ezgif.com/) things work normally. Not sure if that is the issue for you or not (depends if you're using that gif or not and with what screen res etc)
Thanks to sharkfinpin
I've modified the nice t-arc underlay to suit my cabinet, added transparency inside the ball selection and made 2 bar version, one solid and one with transparency.
Added also an alternative version for Visual Pinball system logo.
Zip contains also the pinballx loading gif
underlay_gold.zip