Apologies if this is in the wrong category, couldn’t see one for reporting website bugs 
I long suspected that the practice timer doesn’t record elapsed time correctly when the browser is in the background, and finally confirmed it tonight when I timed it. I started a 15min timer for one of my practice items, then noted the time on the clock, before minimizing my browser and switching to YouTube app (this is on my Android phone). After 20mins on the clock had passed, I switched back to my browser tab with the timer running and it said only 5mins had elapsed!