The two obvious culprits for this kind of thing would be that your nutrient is too basic (strawbs like a pH of 6.5. weakly acidic) or that your roots are too wet. strawberries are (in my opinion) rather hydrophobic and don't tolerate soaking very well.

Check your pH. Make sure your roots aren't too wet.

Perhaps the roots are too wet, I don't know. I am not sure how to fix that though. I started some new plants and hope that when they get big enough, they will replace the dead ones. The PH seems to be ok. Not sure about the food though.

Looking back, I think the problem was that my roots were too wet. I changed the settings on the timer so the water won't be in the tank so long. I lost at least 3 of the plants. The others are doing ok. Somehow fern plants were attached to the rockwool blocks that the strawberry plants grew out of, so I cut them off as well. I've started some new Alpine strawberries to replace the ones that died.