Could they be damping off?
Here's a couple of off site links to check it out...
- http://www.extension.umn.edu/garden/yard-garden/diseases/damping-off/
- https://www.planetnatural.com/pest-problem-solver/plant-disease/damping-off/
you can easily prevent the problem by providing good air circulation. A small fan or simply cracking the lid of the germination tray will suffice.
Thanks @wizardave! I will give these links a look and hopefully I will get a few ideas to try.
welcome