Delta update failure / reliability?

I am using an rpi4-b, I have tried a lot of delta updates. However sometimes I do have checksums related issues which i do not understand.

For instance I have 3 releases: prod-11 prod-12 prod-13
I have already did an incremental update from 11 to 12 to 13. Then later on, when i downgrade to 12 then proceed to an update from prod-12 to prod-11 it does not work with the following error :

2024-05-17 09:38:31 +0000 UTC info: Running Mender client version: 3.5.1
2024-05-17 09:38:32 +0000 UTC info: State transition: update-fetch [Download_Enter] -> update-store [Download_Enter]
2024-05-17 09:38:32 +0000 UTC info: No public key was provided for authenticating the artifact
2024-05-17 09:38:32 +0000 UTC error: Artifact dependency "rootfs-image.checksum" not satisfied by currently installed artifact (c3168cb3219f91996d0d5edc57a4f8e22d874f225e084c090576d02da1d42330 != f67209e129e4e164291b7c9e72178c6ca5f21556e3b678b0f19683c77a43b427).
2024-05-17 09:38:32 +0000 UTC info: State transition: update-store [Download_Enter] -> update-status-report [none]

However when i update once again to prod-13 it works perfectly. How is that possible ?

I do have a read only rootfs with an /etc overlay.
My rootfs is mounted as ro, I checked /proc/cmdline and fstab. I have a symlink from /usr/share/myapp to /data/myapp.

I am afraid that update will fail if my rpi is in the client. So any help would be appreciated.