It looks like https://librecmc.org/librecmc/downloads/snapshots/current/core/targets/ath79/generic/librecmc-ath79-generic-tplink_tl-wr1043nd-v4-squashfs-sysupgrade.bin has been changed (probably along with many other files), but https://librecmc.org/librecmc/downloads/snapshots/current/main/targets/ath79/generic/sha256sums didn't change to match it.
The image you linked to is a core image and the sha256sum is for main images. You would need the corresponding sha256sum for the core image found here : https://librecmc.org/librecmc/downloads/snapshots/current/core/targets/ath79/generic/sha256sums or the correct main image.
Thanks for your reply. You're quite right. I'll need to be more careful about downloading the main image, rather than the core image next time.
So the v1.5.2-20200816 release listed at https://gogs.librecmc.org/libreCMC/libreCMC/releases made no difference to the https://librecmc.org/librecmc/downloads/snapshots/current/main/targets/ath79/generic/librecmc-ath79-generic-tplink_tl-wr1043nd-v4-squashfs-sysupgrade.bin image? Or has the latter not been updated to that release yet?