Using the random expression in a condition will change the value every tick, when what you want is a random interval between spawns.
A possible implementation is using a global variable to keep the value for the interval.
And each time this interval is done, spawn an object and set a new value for the interval. The value is a mix of random and an operation according/depending on the score.
The expression here is just to show how you can do.
It's not a long term viable solution as at some point the value of the score might end giving 0 intervals (which then should spawn each tick).
Anyway, hope this answers your question.