Also speed up tx relay while touching the file anyway.
This should fix the intermittent error AssertionError: Mempool sync timed out:
If it doesn't solve the issue completely, we may also need PR17770, PR18345 and PR18704. These 3 PRs were previous unsuccesful attempts to solve this issue by Core, maybe they are useless or maybe they are part of the solution.
This is a backport of Core PR18752