Just thought I'd share an update. My router worked "fine" using the Vanilla Openwrt on X3000 guide since August, and it's worked great. However, I recently got frustrated by the fact that I was using non-mainline OpenWRT, couldn't install packages, etc, and decided to make a change. I bought a M.2 Phy Adapter and harvested the 5g module out of my Spitz. I was using the Spitz as essentially just a modem, fed into a Peplink router, so I really didn't need the "router" part of the Spitz. The guides on iamromulan/cellular-modem-wiki worked excellent for me to get back up and running with the modem in IP Passthrough to my Peplink router.
This is mostly off topic for here, but it was only done because of the boot issues with the Spitz. If you are using yours in a similar manner to me, moving to just an adapter rather than a router simplifies things. If you have issues, posting on that github is more appropriate than here.