You’re booted from NOR flash.

https://docs.gl-inet.com/en/2/hardware/ar300m/#using-firmware describes how to switch back to NAND firmware.

With NAND flash, that line should look something like

/dev/ubi0_1 on /overlay type ubifs (rw,noatime,assert=read-only,ubi=0,vol=1)

note “ubi” and “ubifs” instead of “mtdblock” and “jffs2”

Edit: The GL.iNet boot loader likely detected three “failed boots” and switched over to NOR boot so that you could access the device. Many people, including I, consider this a good feature, though it requires a sharp eye to see the change. I miss it myself on several devices I work with, GL.iNet and otherwise.