I have experienced a similar issue along these lines. Xiaoxiang App worked flawlessly on my Galaxy S7 for 6 months. Launched, connected and reported live info within about 10 seconds from tapping the icon. Recently got a new Galaxy S20. The app installed without issue, but now takes several tries to get it to connect, and once on the "home screen" its all zeros for up to 30 seconds until all the numbers are populated. Switching to battery view or parameter view? well I have yet been able to see parameter view as it just sits at 0% of 0/59. Battery view takes about 25-30 seconds, then back to homescreen, another 30 seconds or so.
So.. I go back to my S7 and discover that suddenly, it too, is laggy! Takes up to and over a minute to get it to populate and report numbers! Switching from battery to parameter views takes over a minute! SO... what gives here? Tried the rebooting feature, even unplugged the dongle a few times, but now I have very very poor response time on both my phones!!
I'm having flashbacks to the 80's when I tried to download a whopping 500kb file on my 486 computer with a us-robotics 14.4 modem. I click download, go make a sandwich, eat half of it, then check in on the status, and hopefully im at 70-80% complete!!
Very frustrating!!!