I never remove the block_log.index file when replaying and I've not had any issues yet. The --resync arg will start a full resync and the whole process will take much longer to complete, because it will also build the block_log from start by syncing each block.
When I run replay on RPi4, the block_log.index file became very large which resulted in takes all the RPi's storage of 512GB.
This is definitely not normal. The index file only contains the positions and lengths of the blocks in block_log. So it looks like steemd on ARM has a problem with reading the blocks from the log.
Thank you for your opinions. I am contacting a person who succeeded in arch linux for Blurt.
He also said, I have to sync from the start. I will share more when I find a solution.
Great, keep me updated on the progress ;)