Hi,
I attempted to install MM on an new large MM project.
I used the AIY Projects SD image as I wanted to install Google assistant as well and it saves a lot of trouble getting the Voice Hat and Mic to work. Had issues with installing MM2. The rpi auto install would fail on installing dependencies. npm would install but would throw errors on verious packages and not error out.
I installed a fresh Raspian stretch image and that did the same. Dependancies would not install properly and npm install would error out on several items.

Eventially I went back to the AIY projects SD image,
did an apt update and apt upgrade.
REbooted
configured the pi with locale, keyboard, wifi etc
Rebooted
did the mm2 install
rebooted
updated npm as in the other threads here (I had tried this many times before but after rebooting at every stage it worked and updated to v 6.XX )
ran npm start and it worked no problems.

Previous install of MM2 had worked OOB and no issues. Maybe something about v2.4X. Anyway reboot regularly throughout the install process worked for me.
I’ll post pics of my new mirror soon 700x500 Ikea frame with 6mm Mirrorkote glass and Hand made rear frame. Rpi3b with AIY Voice Kit (really great quality mic) works very well.

Cheers

Paul