File blockchain_header gets corrupted about electrum HOT 4 OPEN

do you have old data inside your electrum folder? if so can you still reproduce with everything disabled

I was not able to reproduce with the latest master. Could you please try again

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no old data in folder .electrum-xvg.

new test with master branch:
2 seperate computer (ubuntu18 and debian10), one connected to electrum.marpmedev.xyz, one to node1.verge-electrum.com:
Error after 60 min, next try (after deleting blockchain_header) it takes only 2 minutes up to the error, then 90 minutes.
It looks like the error occur on both computers/wallets at the same time.
I attach an invalid blockchain_header
_blockchain_headers.gz

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File "/home/ben/electrum2/electrum/blockchain.py", line 544, in chainwork_of_header_at_height
work = ((2 ** 256 - target - 1) // (target + 1)) + 1
TypeError: unsupported operand type(s) for -: 'int' and 'str'

reason crash: variable target is str/undefined

540 def chainwork_of_header_at_height(self, height: int) -> int:
........"""work done by single header at given height"""
........ chunk_idx = height // 2016 - 1
........ target = self.get_target(chunk_idx)
........ work = ((2 ** 256 - target - 1) // (target + 1)) + 1
........ return work

494 def get_target(self, index: int) -> int:
........ # compute target from chunk x, used in chunk x+1
........ if constants.net.TESTNET:
................ return 0
........ if index == -1:
................ return MAX_TARGET
........ if index < len(self.checkpoints):
................ h, t = self.checkpoints[index]
................ return t

h,t ---> t = undefined, because of file checkpoints.json (index[0])

[
["00000000007a5b03d0cde55844032c8c890c9e6bac0d7836aad53c9e251f301d", ""],
["0000000009076a32f65518d94c76fd3d281b86dc3185030800ea07ff8ffba559", ""],

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Well we have to somehow adjust targeting for sure. Right now I've disabled the target checks in electrum since bitcoin got a quite easy approach to check em but we have a huge calculcation for upcoming targets and also do we have retargeting each and every block instead of once every 2016 Blocks.

Seems like a huge task to get this all done, but it's also quite necessary in order to ensure a solid working product.

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