InvalidOperationException - EF Instance - Identity Resolution

InvalidOperationException: The instance of entity type 'Vet' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values.

 public async Task<IActionResult> Create(RoomViewModel model)
        {
            if (ModelState.IsValid)
            {
                // Converts the model to a Room object.
                var room = _converterHelper.ToRoom(model, true);

                // Before creating the Room check if there's a room with the same VetId, nulls it if exists.
                var previousRoom = _roomRepository.GetByVet((int)model.VetId).AsNoTracking().FirstOrDefault();
                if (previousRoom != null)
                {
                    previousRoom.VetId = null;
                    await _roomRepository.UpdateAsync(previousRoom);
                }
                
                // Creates Room
                await _roomRepository.CreateAsync(room);

                // Changes the room on the related Vet object if provided.
                if(room.VetId != null)
                {
                    Vet vet = await _vetRepository.GetByIdAsync((int)room.VetId);

                    await _vetRepository.UpdateAsync(vet); //Error occurs at this point.
                }

                return RedirectToAction(nameof(Index));
            }
            return View(model);
        }