Cookie (null) loading web-vault

by upgrading web-vault to v2023.5.0 I’m noticing an unexpected behaviour.

Since v2023.4.2, I’ve always injected a cookie to the client by apache, using this rule in httpd conf file:

<Location />
Header append Set-Cookie "usermail=%{mail}e; path=/; Secure; Max-Age=900"

It has always worked fine until now. Installing the new v2023.5.0 web-vault update, this cookie turns into (null) value, few moments after the page is loaded. If I refresh the page, browser gets the desired value back by the server. It happens in different browsers (chrome, firefox, edge).
This cookie is pretty important for further actions client-side.

Is there a way to fix this according to the new v2023.5.0 release?

Thank you very much