Lectora version 18 titles are not backward compatible. Once you have saved your title in 18, it should not be opened in Lectora version 17.
For the pink screens / objects issue, there appear to be some objects that when they originated in a Lectora 17 title, then have been saved in Lectora 18, then again opened in 17 result in the pink color. Do you possibly have a back up version from 17 that is untouched?
Would you please let me know your support case number? Thank you