This takes about 5 seconds through the web player. On the mobile app, it loads for about 10 - 15 seconds. stops, waits 15 seconds, then loads again and loads the records. I have put this in OnStart, OnVisible, and on the Items of the gallery itslef and it does the same thing: Overall, 45 seconds on mobile player.
ClearCollect(opps,AddColumns(SortByColumns(Filter(Opportunities,_ownerid_value = LookUp(Users,domainname = User().Email,systemuserid),_customerid_type = "accounts"),"createdon",Descending),"AccountName",LookUp(Accounts,accountid = _customerid_value,name)))
How many records do you have to load for this formula?