The backup configuration file in V5.2.0-5.2.4/V5.3.0-V5.3.1, which contains certificate configurations, may not be restored properly, causing configuration lost. After upgrading to V5.3.2, please discard the old V5.2.x/V5.3.x config file, backup the config file in V5.3.2 again; it should work, now.
Adjust boot partition
To upgrade image for VM platfroms, because of the boot partition size limit before 5.1.x, please be sure to upgrade to 5.1.x image first to adjust boot partition size, then upgrade to 5.2.x and 5.3.1, or else it will report "Unmatched partition size" error when upgrading.
No such issue for physical platforms.