Task generation across a version is serial, so one task performing generate.tasks can block progress of another. 

In many patches, task generation extends the task by 10 minutes, and in bad cases by 30+.

https://parsley.corp.mongodb.com/evergreen/mongodb_mongo_master_linux_64_debug_required_resmoke_tests_8c2d4d7e6aa2b901c0e993c1bad0139870c34f52_26_03_03_12_33_33/0/task?bookmarks=0,2461,2463&shareLine=2458

The advice from DEVPROD-27621 is that all task generation is consolidated in to a single instance.