yarn install --mutex network:42424 --non-interactive

lerna ERR! yarn install --mutex network:42424 --non-interactive exited 1 in 'selenium-ide-extension'

Probably the reason is in https://github.com/lerna/lerna/blob/master/src/NpmUtilities.js#L66.

I assume that lerna is running more than one node_modules installation in parallel.

Yarn may fail if it runs yarn install in multiple processes because they may be reading/writing to common cache folder.
A way around is to run yarn with --mutex network option.
But be mindful to run with a non default port otherwise top level Yarn with --mutex network will never allow this script to start.

Sounds like --mutex network:<nonDefaultPort> (docs) is the ticket.

Concurrency

and --mutex

When running multiple instances of yarn as the same user on the same server, you can ensure only one instance runs at any given time (and avoid conflicts) by passing the global flag --mutexfollowed by file or network.

When using file Yarn will write/read a mutex file .yarn-single-instance in the current working directory by default. You can also specify an alternate or global filename.

--mutex file
--mutex file:/tmp/.yarn-mutex

When using network Yarn will create a server at port 31997 by default. You can also specify an alternate port.

--mutex network
--mutex network:30330

Verbose output

with --verbose

Running yarn <command> --verbose will print verbose info for the execution (creating directories, copying files, HTTP requests, etc.).