A321 Captain reported an ECAM indicating a malfunction with one of the main cabin doors during climb. The aircraft returned to land at the departure airport and maintenance determined an issue with the slide girt bar positioning in the door track.

Narrative

We departed early and were climbing out through approximately (~XA20Z) FL210 and received the ECAM for Door R Fwd Door. First Officer was PF and Captain worked through the ECAM. QRH X-X was competed and cabin pressurization was normal.Other indications were the Doors SD (System Display) showed amber for the door and all slides armed.Captain called the purser to discuss the condition of the door. They informed me that the FAP (Flight Attendant Panel) had a cabin door message; the 'slide armed' light was illuminated; and the mechanical door indicator was showing half closed. It was only half visible.Captain called dispatch for a patch to maintenance. It was confirmed that the QRH was completed. I conveyed that the pressurization was normal and the mechanical indication was not fully visible; but partially. M believed we needed to land for maintenance. Despite ZZZ1 on our right and ZZZ2 off the left; they wanted the aircraft back in ZZZ to allow our own Maintenance to look at the door. While continuing to coordinate with dispatch; First Officer coordinated return routing to ZZZ with ATC. During the initial decent; the ECAM message disappeared. It was confirmed with the purser that the mechanical indicator was still showing half green. Further contact with Maintenance confirmed their desire to continue back to ZZZ.Dispatch reroute release was received. Diversion checklist completed and overweight landing checklist completed. Customers and crew were notified of the need to return to ZZZ.Inbound to ZZZ; the APU was started to help burn down weight (as well as for procedure of the overweight landing). After setting up the approach and briefing all contingencies; to include overweight landing procedures; Captain took control of the aircraft. No emergency was declared as landing weight was calculated to be very close to or even below max landing weight at touchdown. At touchdown; the vertical rate was well below the required 350 ft/min; and the VSI did not register a descent rate at all. Maximum reverse was used in lieu of brakes until 70 knots. Fans were engaged upon clearing the runway and a max temp of 95 was achieved. Touchdown weight was 172;400# with a max landing of 171;519#. Customers were deplaned as the aircraft was taken out of service. Over the course of several hours work; Maintenance was able to determine the issues with the door. The slide apron attachment to the girt bar was bunched up and prevented the girt from maintaining the flat locked position. Also; the door lock pin tracks showed some rust and interfered with smooth operation of the locking detent mechanism. The slide and girt bar were adjusted; and the pin tracks were cleaned and lubed. The door tested appropriately with all electronic and mechanical indications and was returned to service. Regarding the overweight landing; Maintenance stated that no report was generated by the landing and an overweight landing inspection was not required.