The problem isn't the missing "quote", Rainmeter is fine with that in this case, we just assume one...
A regular expression Substitute=".*":"" is a fatal recursion. An endless loop. You are saying "change zero or more of any character into an empty string". It can never finish doing that... There will always be "zero or more" characters left for it to change.
There are any number of ways to get regular expression tied up in knots. Nothing we can do about that. Regular expression is what it is. Think of it as a "teaching moment"...
If you make that Substitute=".+":"" then it's ok. That is "change one or more of any character into an empty string".