I agree with what's been offered as a remedy. I am running Toast 15 in Mojave, and all is well on my 2009 cMP. While not as comprehensive as Toast, Disk Utility can take care of normal writing tasks, just like it always has. I would suggest you start looking at your crash reports. I have had problems with some of the Toast applets not working correctly after aging a bit, but never an uncorrectable situation. The first thing I would do is to delete Toast as completely as possible and reinstall it. If it crashes, go to the Console and find out why. It may just be a resources issue, despite how slow a DVD burner is.
While we're on the subject of disk burning, I'm wondering if "burners" would report back on failing media, M-Discs, and other pertinent issues. I have an external LG Blu-ray burner that has M-Disc capabilities (<$150 8 years ago) Besides the M-Disc media, I have used almost every brand in most every format. In the last 5+ years, I have used only the top line Verbatim disks. However, many of them now have problems, especially the BR disks. But it was random as other disks made at a similar time with the same media are not damaged. All of them were stored properly in the same place. ???? As for the longevity of the M-Discs, I have not yet seen a problem, and they are my disk of choice for archival use.
As for Toast, I got the add-on Video burner software as I have had in the past. It allows you to create video disks. I have done a bunch of stop action animation over the years, and wanted a way to be able to distribute hard copies. This Toast add-on does that very well, and will even burn a BR quality disk onto a twenty-nine cent DVD. It is too short for most movies, but perfect for my video animations. Now that online can handle the HD quality formats, it's rare that I make one today.
I'd love to hear from others about their current burning standards, disk choices, etc.