I have 2 2007 iMacs with slightly different radeon graphic cards. No problem with the first, but the second shows a blanched, white, semi transparent graphics only when it resumes after a suspend!

Elementary Juno built on Ubuntu 18.04.2 LTS
Imac 2007 Core 2 duo. AMD/ATI RV610/M74 Mobility Radeon HD 2400 XT.

Any solutions to this problem?