The 'flags' field should be exactly either 0 or 128: the "Issuer Critical Flag" is bit 0 of the flags field, and not the _value_ of this field.
Unsurprisingly, many people get that wrong (with values encountered ranging from 0 to 250, with no clear indication what people might think those values mean):
RFC8659 defines three different properties: 'issue', 'issuewild', and 'iodef'. That's it.
(CA/B Forum Ballots SC13 and SC14 added 'contactemail' and 'contactphone', but those aren't part of the RFC, and I only encountered 741 and 23 uses of these respectively, so let's ignore them.)