Sorry that Lightroom takes a long time to add images on your Android device. Which version of Lightroom are you using and on which mobile device? I'd recommend that you clear the app cache and let us know if that helps. Navigate to the below menu in Lightroom app and select "Clear Cache".
I have Lightroom 5.1 on a Redmi Note 7 and don't think clearing cache is going to solve things, Since I uninstalled a reinstalled the app and the problem persisted.. the problem is to find pics by folder in the device... It finds them but it takes (no joke) 4 to 5 mins to load.. I don't have that many images to load.. so the other option that came to my mind is that recently I placed a 128gb micro SD.. wich doesn't have any pics.. but maybe Lightroom is taking that extra time searching there.. this is completely a guess