To fix this issue, follow the steps below. 

1) Manually type in a tribute type in the Tribute Type field (e.g. In Honor Of, In Memory Of, etc.). Doing so will unlock the Honor/Memorial search button.
2) In the Honor/Memorial field, search for and select the desired constituent record.
3) If the constituent already has a tribute on their record, the tribute will appear in the Tribute field > Click OK to link this tribute to the donation. If that constituent record doesn’t already have a tribute on the Honor/Memorial tab, clicking the folder brings you to the constituent record to add one.