I also have the same problem. Phone just become useless when come to multitasking. I'm so disappointed.
I think they need to disable all that battery savers and go for 'high performance' mode.
I even can't scroll in Facebook App...
Strange complaint cause i actually felt the opposite. Phone became faster and more responsive. Maybe some apps that haven't yet updated for oreo might causing problems?
chrome , phone,message is also slow !!!
After 141h of uptime multitasking doesn't work at all. It restarts apps everytime.