This bug was fixed in Patch 1.44.88.
When placing wallpaper (and sometimes floor tiles) the game lags extremely and I can hardly place anything
Patch 1.44.83 only somewhat helped with this issue so it’s still treated as open bug.
According to SimGuruNick on twitter, the lag only occurs on blocks attached to roofs.
Delete every roof object first, then place the wallpaper
Be aware that this is only a temporary workaround until Maxis can fix the issue permanently.