I have ZBT WE826 (16M) (MT7620A).
After sysupgrade using custom image, from 18.06, to TRUNK, the filesystem is corrupted.
Fri Feb 28 23:54:46 2020 kern.notice kernel: [ 0.000000] Kernel command line: console=ttyS0,115200 rootfstype=squashfs,jffs2
Fri Feb 28 23:54:46 2020 kern.info kernel: [ 0.762753] jffs2: version 2.2 (NAND) (SUMMARY) (LZMA) (RTIME) (CMODE_PRIORITY) (c) 2001-2006 Red Hat, Inc.
Fri Feb 28 23:54:46 2020 user.notice kernel: [ 9.122708] mount_root: jffs2 not ready yet, using temporary tmpfs overlay
Fri Feb 28 23:55:12 2020 kern.warn kernel: [ 41.314537] jffs2_scan_eraseblock(): End of filesystem marker found at 0x0
Fri Feb 28 23:55:12 2020 kern.warn kernel: [ 41.337428] jffs2_build_filesystem(): unlocking the mtd device...
Fri Feb 28 23:55:12 2020 kern.warn kernel: [ 41.346718] jffs2_build_filesystem(): erasing all blocks after the end marker...
Fri Feb 28 23:55:12 2020 kern.warn kernel: [ 41.346745] jffs2: Erase at 0x00b92000 failed immediately: errno -22
CPU: 0% usr 100% sys 0% nic 0% idle 0% io 0% irq 0% sirq
Load average: 1.27 1.20 0.69 2/38 1267
PID PPID USER STAT VSZ %VSZ %CPU COMMAND
1050 1049 root R 1120 1% 73% mount_root done
223 2 root RW 0 0% 26% [spi0]
Sat Feb 29 00:04:38 2020 kern.notice kernel: [ 607.513938] jffs2: notice: (1050) jffs2_build_xattr_subsystem: complete building xattr sub system, 0 of xdatum (0 unchecked, 0 orphan) and 0 of xref (0 dead, 0 orphan) found.
Sat Feb 29 00:04:38 2020 kern.warn kernel: [ 607.679388] overlayfs: upper fs does not support tmpfile.
Sat Feb 29 00:04:38 2020 daemon.info mount_root: performing overlay whiteout
Sat Feb 29 00:04:38 2020 daemon.info mount_root: syncronizing overlay
Sat Feb 29 00:04:38 2020 daemon.err mount_root: failed to sync jffs2 overlay
There is another error report with similar symptoms:
Going back to 18.06, as no problem there.