Data leak error when upgrading from 3.4 to 3.20?

I have been using Express 3.4 with good success for a while.

I'm not quite ready to make the move to Express 4. However, I think it would be nice to upgrade to the latest Express 3 before moving to 4.

So, I have updated my app to use Express 3.20.

Now: When I run my app on express 3.4, the memory usage for each process in pm2 tends to hover in the mid 200, with a low 300MB range.

As soon as I upgraded to 3.20, memory usage started increasing by over 600MB in less than an hour for each process, at which point everything went wrong.

Going back to 3.4, I have confirmed that memory usage remains in the mid-200s.

Changing express versions is the only modification I've made.

I'm wondering: Is there a known issue / change of some kind between 3.4 and 3.20 that could cause a memory leak?