Several after hours prices and relative changes seem to be random, no link between the previous close and the pre market ones
I would agree. After hours quotes need to have a time and day stamp. That quote gets deleted so nothing appears when regular market trading begins.
Very unreliable. I understand data is not guaranteed, but random is a different story. There have been several times I excitedly logon to my brokerage account finding the after hours quote cannot be found even in the day trading range...
Customer support service by UserEcho