Available times on drop-down menu are not displayed properly on admin side

I’m having an issue when adding a new appointment from the admin: when viewing the appointment on the list, the start time is displayed properly, but if checking the appointment details the start time is displayed as ‘Unknown’. The steps I followed to add the new appointment were: fill in the details, select the time and date, change the status to Confirmed and save the appointment.

After a few tests we’ve noticed that this might be a random issue because not all the new added appointments had it. This seemed to be only related to the services that exceed in time when choosing a start time (so, if the service has a duration of 3h, start time is set to 12pm and the available time ended at 13pm, then the appointment will display the ‘Unknown’ start time when checking its details), but also some previously created appointments that did not exceed on time had the issue as well.

During the chat we were able to replicate this on a testing site when just having Appointments+ and the WPMU DEV dashboard plugins active on the site, running Twenty Seventeen theme and with NO add-on active on Appointments+: the start time was displayed as ‘Unknown’ when viewing the appointment details, but was properly displayed when viewing it on the list of all appointments for appointments for services with a time duration that exceeded the hours left after the selected starting time.