I can't move a track forward or backward

I’'m using Audacity 2.1.3 with Windows 10 but also the most recent release on my Macbook Pro at home. I download podcasts as MP3 files, save them to my hard drive and use Audacity to open and create tracks by inserting labels every 10 minutes or so. I use the Export Multiple feature to save the tracks to an SD card. I then put the SD card in an old cell phone that I don’t use for calls and listen to the podcast with the Musicolet app while driving to work and back. Musicolet a simple no-frills app that allows me to play MP3s a phone. The purpose of the tracks of course is that I want to listen to the podcast in sections.

This more-or-less works, but often when I tap the forward track triangle it goes to the track I am currently listening to. Also if I tap the back triangle it goes to the track I am listening to, or some other track other than the previous one.(See screenshot.) Am I doing something wrong? Is the problem Audacity or the app?
musicolet screenshot.png

By default, Audacity uses VBR encoding for MP3s (because VBR gives better quality for the same file size compared with CBR encoding). Some media players have trouble with VBR encoding, so it may be worth trying CBR encoding. To do that, in the Export dialog screen, select “Constant” as the “Bit rate mode”.

Thank you for your reply. I am not seeing where to change the bit rate mode on the Export screen.

The selected format in that picture says “WAV (Microsoft) signed 16-bit PCM”.
To set the MP3 settings and export as MP3, you need to select MP3 as the export format.