Backup procedure "Save mtdblock contents" downloads are incomplete

On a Belkin RT3200 running stock firmware "1.0.01 build 101415 OCT 14, 2020" if I follow the Device flash complete backup procedure by flashing openwrt-22.03-snapshot-r19338-ae64d0624c-mediatek-mt7622-linksys_e8450-ubi-initramfs-recovery.itb (or openwrt-22.03.0-rc6-mediatek-mt7622-linksys_e8450-ubi-initramfs-recovery.itb built from dangowrt/owrt-ubi-installer@e966acf with an edit to use 22.03.0-rc6 - same result) then download the mtdblock contents from System -> Backup / Flash Firmware, the downloaded files are incomplete:

Device	Size	Download Size
mtd0 (bl2)	524,288	524,288
mtd1 (fip)	1,310,720	802,816
mtd2 (factory)	1,048,576	0
mtd3 (ubi)	131,072,000	131,072

Note: The Size column is the size in bytes, as reported in /sys/class/block/mtdblock*/size (multiplied by 512) and of the files produced by dd if=/dev/mtdX.

The downloads are the same on every attempt in both Firefox and Chrome.

The Content-Length header of the HTTP response indicates the correct size, but the response is aborted before the download completes.

logread contains the following messages when an attempt was made to download mtd1:

Tue May 31 13:53:49 2022 kern.warn kernel: [ 1544.984764] print_req_error: 37 callbacks suppressed
Tue May 31 13:53:49 2022 kern.err kernel: [ 1544.984772] blk_update_request: I/O error, dev mtdblock1, sector 1568 op 0x0:(READ) flags 0x84700 phys_seg 15 prio class 0
Tue May 31 13:53:49 2022 kern.err kernel: [ 1545.000990] blk_update_request: I/O error, dev mtdblock1, sector 1576 op 0x0:(READ) flags 0x84700 phys_seg 14 prio class 0
Tue May 31 13:53:49 2022 kern.err kernel: [ 1545.012171] blk_update_request: I/O error, dev mtdblock1, sector 1584 op 0x0:(READ) flags 0x84700 phys_seg 14 prio class 0
Tue May 31 13:53:49 2022 kern.err kernel: [ 1545.023347] blk_update_request: I/O error, dev mtdblock1, sector 1592 op 0x0:(READ) flags 0x84700 phys_seg 13 prio class 0
Tue May 31 13:53:49 2022 kern.err kernel: [ 1545.034522] blk_update_request: I/O error, dev mtdblock1, sector 1600 op 0x0:(READ) flags 0x84700 phys_seg 13 prio class 0
Tue May 31 13:53:49 2022 kern.err kernel: [ 1545.045697] blk_update_request: I/O error, dev mtdblock1, sector 1608 op 0x0:(READ) flags 0x84700 phys_seg 12 prio class 0
Tue May 31 13:53:49 2022 kern.err kernel: [ 1545.056903] blk_update_request: I/O error, dev mtdblock1, sector 1616 op 0x0:(READ) flags 0x84700 phys_seg 12 prio class 0
Tue May 31 13:53:49 2022 kern.err kernel: [ 1545.068109] blk_update_request: I/O error, dev mtdblock1, sector 1624 op 0x0:(READ) flags 0x84700 phys_seg 11 prio class 0
Tue May 31 13:53:49 2022 kern.err kernel: [ 1545.079283] blk_update_request: I/O error, dev mtdblock1, sector 1632 op 0x0:(READ) flags 0x84700 phys_seg 11 prio class 0
Tue May 31 13:53:49 2022 kern.err kernel: [ 1545.090458] blk_update_request: I/O error, dev mtdblock1, sector 1640 op 0x0:(READ) flags 0x84700 phys_seg 10 prio class 0
Tue May 31 13:53:49 2022 kern.err kernel: [ 1545.143235] Buffer I/O error on dev mtdblock1, logical block 196, async page read
Tue May 31 13:53:49 2022 kern.err kernel: [ 1545.151257] Buffer I/O error on dev mtdblock1, logical block 196, async page read
Tue May 31 13:53:49 2022 kern.err kernel: [ 1545.158954] Buffer I/O error on dev mtdblock1, logical block 196, async page read

Are these a result of the non-UBI ECC errors mentioned in the Installation section of the OpenWrt ToH device page? If so, should the backup instructions advise avoiding LuCI for stock firmware? If not, I'd appreciate suggestions for further debugging or whether I should report this bug to the OpenWrt project.

Thanks for all your work on this project! Kevin

dangowrt / owrt-ubi-installer

Backup procedure "Save mtdblock contents" downloads are incomplete #112