This appears to happen exclusively on mac hosts (e.g. failure  The install failure shows up as something like:

 
[2022/01/21 15:09:17.225] npm ERR! Unexpected end of JSON input while parsing near '...XnH1paQyQwQp5Ba2MYZau'
[2022/01/21 15:09:17.243] npm ERR! A complete log of this run can be found in:
[2022/01/21 15:09:17.243] npm ERR! /Users/mci/.npm/_logs/2022-01-21T15_09_17_225Z-debug.log
[2022/01/21 15:09:17.249] Now using node v12.22.9 (npm v6.14.15)
[2022/01/21 15:09:17.249] Command failed: command encountered problem: error waiting on process '268fdcae-a028-45d6-818c-78b08d4131c1': exit status 1
 
Which then causes, after tests have run,
 
[2022/01/21 15:23:01.791] .evergreen/run-async-std-tests.sh: line 22: junit-report-merger: command not found
[2022/01/21 15:23:01.791] Command failed: command encountered problem: error waiting on process 'e1a09402-1834-497e-ab12-7f66d9a7607d': exit status 127
 
At the very least, the install failure should cause the task to fail as a system failure; ideally we'd figure out why the install occasionally fails and fix that.