Sending an invitation fails when leaving the message field blank. The SEND button gets disabled but the message never gets queued. I do not see any debug messaged that could be related to the issue, so it most probably is a client side (JS) issue (an “Invalid data” is thrown - in PydioMailer.js [line 229] because of message is empty.
if (!this._subjects.length && !this.templateId || !this._targets.length || !this._messages.length) {
throw new Error('Invalid data');
}
I do not actually understand why a message is required as it can only be used to provide additional information - it is perfectly possible to go without 
As the error is not shown to the user, he will never know whether or not the sending succeeded.
