There was this bug - https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/838208
There are some discussions (other links/searches) about Compiz, and separately discussions about compositing, that in either when they were disabled it was solving it.
It was saying how where "fancy effects" were being used by desktop environment, or apps (only Firefox was specified in one post, but in others no apps were specified), then this was causing the spike in CPU useage from 60 til 100% and slowness/lag after suspend/sleep, not improving unless reboot was done. After which still being higher than usual until the feature was disabled. (summary info from a multiple links)
Have you tried -
Menu > ALL > Window Manager Tweaks
In the GUI select the Tab named "Compositor" untick the first item named "Enable display compositing"
Click close.
Does this help it improve or not ?
There are some discussions (other links/searches) about Compiz, and separately discussions about compositing, that in either when they were disabled it was solving it.
It was saying how where "fancy effects" were being used by desktop environment, or apps (only Firefox was specified in one post, but in others no apps were specified), then this was causing the spike in CPU useage from 60 til 100% and slowness/lag after suspend/sleep, not improving unless reboot was done. After which still being higher than usual until the feature was disabled. (summary info from a multiple links)
Have you tried -
Menu > ALL > Window Manager Tweaks
In the GUI select the Tab named "Compositor" untick the first item named "Enable display compositing"
Click close.
Does this help it improve or not ?