Somewhere between this commit on master:

• f0e5295 (tag: v2_1_50_0, tag: 2.1.50) Start of 2.2 development, updated version to 2.1.50

and this commit:

• 7b86fd9 (tag: v2_1_51_0, tag: 2.1.51.0, tag: 2.1.51) Increase lustre version to 2.1.51

master appears to have lost the ability to mount 2.1 servers.