My first impression is that your issue does not go to Premiere Elements 12/12.1 burn to process, but rather to the specifications of the players and choice of brand/type and labeling for the DVD disc.
1. Do the specifications of the players list your DVD type and formats on that DVD type as supported? Do these discs have labels? Are they the paper kind?
2. Are dealing with Philips and Panasonic players in your own home, or are these players in the homes of people to whom you gave your DVD-VIDEO on DVD disc?
3. When Premiere Elements generates a DVD-VIDEO on DVD disc, the disc contains an OpenDVD Folder and VIDEO_TS Folder. There are rare instances where the disc needs that VIDEO_TS Folder plus an AUDIO_TS Folder for disc-player compatibility. To test this out
a. Take the Premiere Elements Timeline content to burn to folder. Take the VIDEO_TS Folder from the burn to and an AUDIO_TS Folder that you create into the free ImgBurn to get your DVD-VIDEO on DVD disc. You create this Audio_TS Folder by creating a new empty folder on the computer desktop and naming it AUDIO_TS.
Please review and consider, and supply more information. Any questions or need clarification on the above, please do not hesitate to ask.