Following up on this:
InspIRCd supports a large number of IRCv3 options that can affect the format of server messages sent to a client. This includes the channel history messages sent to a user on joining a channel that has +H enabled.
I have installed InspIRCd and enabled various combinations of IRCv3 options but have not been able to reproduce this issue so far.
I would need to know the IRC network you are using in order to test this out.
Alternatively, please post the CAPS messages you see when you first connect to the server. They will look like this:
Caps supported: account-notify account-tag away-notify batch cap-notify chghost echo-message extended-join invite-notify message-tags server-time tls
Caps set: account-notify account-tag away-notify batch cap-notify chghost extended-join invite-notify server-time