I seem to resolve it myself, but it took some work. I made a copy of the site in a test environment to deactivate all plugins again and changed themes. Then I could edit the ticket. But I did need to use the Genesis theme, so turned it back on and started looking at the function.php file & by process of elimination I edited the same code mentioned in this thread: https://theeventscalendar.com/support/forums/topic/tickets-reduced-to-0-and-cannot-edit-existing-tickets/
I commented out all that I was not using such as below and then it worked. Maybe this is something to look into if it has happened not just to me.
// ‘Tribe__Tickets_Plus__Commerce__EDD__Main’,
// ‘Tribe__Tickets_Plus__Commerce__Shopp__Main’, // As of ETP v4.0 Shopp will generate errors when referenced, if not active. Uncomment this line if you have Shopp Active
// ‘Tribe__Tickets_Plus__Commerce__WPEC__Main’,
‘Tribe__Tickets_Plus__Commerce__WooCommerce__Main’