Enabling additional tests in JMeter reduces number of samples

I have a JMeter Test Plan with many copies of almost exactly the same test. In each case there is a variable that is slightly different.

Here is the configuration:

There are two sets of user variables. There is a top level user variable list, that contains maximum_runs and there are Test Fragment level user variable lists with the User Defined Variable add_users, which goes up by 10 for each test case. users is a static 10.

I set maximum_runs to 100 and disable all but one Test Fragment. This gives me a number of samples = 100 for each Fragment. I enable a second Test Fragment and I still get 100 samples. But as soon as I enable the third Test Fragment my number of samples drops to 90. 4th, 80. But on the 5th one it goes right back up to 100 and the cycle starts over again. I don't see anything wrong with my math so I believe it to be something about how JMeter uses jexl2 or maybe variables are being changed due to the number of Fragments running? I really need to be able to run this with the same number of samples no matter how many Fragments are running. Ah, note, I have Run Thread Groups consecutively (i.e. run groups one at a time) in Test Plan checked.

I had a similar issue with one application. 1 out of 4 test components just would not go up more, than 50 percent of required users.

The problem was that component was a memory eater and when it reached the maximum heap it did not let the other threads in that component to ramp-up. But just a long shot.