I did not test your file... But in a NON-converted file completely built in FM12 from scratch... Extreeeemely simple data structure... using the data viewer and the script debugger together in FM12, it was sooooo slooooow that I would consider them unusable.
I could not even imagine what this would be like with a complex financial app. I could probably build a solution as fast as this Debugger/DataViewer combo is displaying in FM12... I never encountered anything like this in FM11 or earlier.
Yes, I can confirm that with your test file yields extremely slow results in 12 where the same test file in 11 did not. I can also tell you that I haven't had any problem with the Data Viewer and Script Debugger open simultaneously in 12. I stepped through several of my scripts in several converted-to-12 solutions and everything worked as expected.
Your test file had 180 fields on a layout and the test script references all these fields plus about 180 variables. When I disabled all but the first 20 fields and variables in your script, speed returned to normal. So it appears that the problem is related to the large number of fields and variables referenced in the script.
Ann Arbor, MI
I got similar results.
I also tried it on a duplicate layout where I removed all the fields; and got the same results.
I note that you are using the classic theme; thus eliminating the theme/conditional formatting argument (for this test anyway)
It would be very interesting if we could get Honza's optimizer tool to evaluate this.
Both files seem to be fast without the debugger on.
The calculation engine seems to be making itself very busy even when it shouldn't.
Looks like a square or even cube law phenomonon. Duplicate the test script, but then remove half the set variable script steps and compare results.