Mail app 0.11.0 not displaying some mail content correctly

Installed and activated the mail app today on NC 14.0.3 NCPv66.4 (NUCi5box Debian9 curl installer)
Adding mail accounts works well and mail gets displayed fine, but for one or two emails, received from a regular supplier, send without any encryption, displaying normal in Thunderbird Version 60.2.1, _64bit
but looking garbled in FirefoxQuantum 63.0 (64-bit) and Chromium v. 70.0.3538.77 (Official Build) Built on Ubuntu , running on LinuxMint 18 (64-bit).
As said text is displays fine in Thunderbird. This is what it looks like in browsers

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Not sure if related, log shows this error

TypeError: Argument 2 passed to OCA\Mail\Http\AttachmentDownloadResponse::__construct() must be of the type string, null given, called in /var/www/nextcloud/apps/mail/lib/Controller/MessagesController.php on line 266

/var/www/nextcloud/apps/mail/lib/Controller/MessagesController.php - line 266:

OCA\Mail\Http\AttachmentDownloadResponse->__construct("--alternati ... n", null, "application/octet-stream")

/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php - line 166:

OCA\Mail\Controller\MessagesController->downloadAttachment(2, "SU5CT1g=", 1, 1)

/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php - line 99:

OC\AppFramework\Http\Dispatcher->executeController(OCA\Mail\Con ... {}, "downloadAttachment")

/var/www/nextcloud/lib/private/AppFramework/App.php - line 118:

OC\AppFramework\Http\Dispatcher->dispatch(OCA\Mail\Con ... {}, "downloadAttachment")

/var/www/nextcloud/lib/private/AppFramework/Routing/RouteActionHandler.php - line 47:

OC\AppFramework\App::main("OCA\\Mail\\ ... r", "downloadAttachment", OC\AppFramew ... {}, { accountId: ... "})

OC\AppFramework\Routing\RouteActionHandler->__invoke({ accountId: ... "})

/var/www/nextcloud/lib/private/Route/Router.php - line 297:

call_user_func(OC\AppFramew ... {}, { accountId: ... "})

/var/www/nextcloud/lib/base.php - line 987:

OC\Route\Router->match("/apps/mail/ ... 2")

/var/www/nextcloud/index.php - line 42:

OC::handleRequest()

This is a bug -> issue tracker https://github.com/nextcloud/mail/issues/1107