Nested loops can work in Thunkable but there are quite a few components that take too long to complete their code and don’t work inside of loops. You’re using a stored variable which is a slower method of storing/retrieving data in Thunkable. I wonder what happens if you use an app variable?
It’s very possible that you’re going to need to add some Wait blocks (possibly just wait 0 seconds) within the loop block(s) to slow things down.