You can use the DEBUG=true env variable too to perhaps see more details

DEBUG=true lein uberjar

So I ran my own leinigen build to debug and determined it was failing at eval.sh, which runs a java command. I ran that java command with -verbose flag and it gave me a little more info. the build is hanging when [class, load] is occurring. it loads 4 in reasonable time but each class load after takes significantly more time [12.521 s, 12.521 s, 13.109 s, 13.308 s, 41.109 s, 191.967 s, 431.966s, 10338.197 s, 12491.966 s]

i also tried many different jvm versions just to rule that out, but the same issue. on the bright side im a little more familiar with leinigen internals

i did test with a blank project with the parent dependency that the class load was slow on and it seems to be related to that dependency. so at least i narrowed it down. it is kind of odd that it continues to "work" (no printed errors) but it just takes several hours for each one.