Has been working for months and months and months. No code changes. Suddenly I get:
app:3852019-11-05 11:27:39.512 am errorgroovy.lang.MissingMethodException: No signature of method: static java.lang.Float.parseFloat() is applicable for argument types: (java.math.BigDecimal) values: 
What app and if you click on the app:385 what app is that ?
No info at all to help you.
Just based on the error:
the method Float.parseFloat has a definition of
public static float parseFloat(String s)
That means it takes a string as a parameter. In your log, the parameter is of the type BigDecimal and that method has no idea on how to convert such type into a float.
Could be several reasons for that and as @Terk and @anon61068208 said, much more information is needed.
Start with what kind of app is it?
It might be that the app hasn't changed but that a device that supplies the value 69 was previously using a string and now is using BigDecimal.
I get the groovy error message on my Go Control Thermostat device. Just started happening.
That is a completely different error than what the OP started with. I’d suggest to open an individual topic for that to not mix up two different issues
How is this different? other than one shows up under an App and the other is a device.
Your problem is with a built in driver that needs to be looked at. Also your problem indicates an issue with a variable that is null. His problem is with a so far unknown app. Yes, they are both errors but of two different natures
That certainly seems to be the case. I'm no groovy expert, it's an app that interfaces with the API for my Rheem EcoNet thermostat that I kind of cobbled together.
To make matters more complicated I target it remotely from Home Assistant with MQTT. In that scenario it is working, I guess because its getting a string from MQTT. It's only when changing temp from the hubitat driver on hubitat that I get the float/bigDecimal error above.
I fixed it by forcing the bigDecimal with .toString() which then gets properly converted to a float.
I swear this used to work and something must have changed, but now I'm not so sure... fixed though.