ffmpeg concat introduces a/v sync problem
Run

ffmpeg -i titlefile.mp4 -vf setdar=16/9 -video_track_timescale 29971 -ac 1 newtitle.mp4


and then run concat with the new title video.

Modern containers like MP4 have Presentation TimeStamps, which are denominated with reference to a timebase. So, if the timebase value is 1/500 and a frame's PTS is 200, then that tells the video player to show that frame at 200*(1/500) = 0.4 seconds. The tbn values shown in the readouts are the reciprocals of this timebase. Now, the concat demuxer, due to a design oversight (or choice!?) does not rescale the PTS values so that all inputs have frames with PTS using the same timebase. Your two videos have different TBs, and so the long video after the concat is being sped up. The difference is perceptually invisible - except for the audio drift. That tbn value is for the video stream. Audio streams have their own timebase, related to the sample rate, which is the same here.