Got the SBA EIDL increase email today. Responded with needed info. Didn't get an auto reply or confirmation email for the first hour. (checked all folders)
I noticed that when I clicked on the email address on the SBA EIDL increase email in order to send the request, it put a '+' ahead of the email address when composing the message. IINM GMail ignores anything following a + in an email address, so your email might have not been sent altogether. IDK if ignoring + on the email address also applies to outbound email. In any event, I suspect that might be the issue.
I just sent email increase requests for 3 EIDL loans I have. I didn't receive any auto response yet.