The "Sold Out" of Tickets depends on the "Ticket Type" you choose in Payment Form.   (Extract from release notes: 8.6 Release  Events  Correct Issue when “Max No. Per Ticket Type” specified would incorrectly mark ticket types as sold out).The corrected issue is for "Max No Per Ticket Type" in the Payment form.  Normally the reason for tickets sold is due to  specifying "Max No. Tickets Available" at the Payment form level and  having Event Type as  "Tickets Only". Please specify Max No Ticket Available at the Payment Option level if  you are using Event Type -Ticket only in Payment Form Level.  If you  change the Event Type-" Ticket and specify all attendees" it should all  work.