customers getting error:email and password not recognized.

[ldttex]

www.itsaquiltthing.com version 1.5.5d. original installation 1.3.7 upgraded by webmaster. php 7.0.33

Error started happening a couple o of days ago...multiple customers (possibly all?) webmaster suggested they clear cache and cookies, and reset password...did all that...still getting error...

Most customers not able to log in. A couple who got logged in tried putting things in their cart, only to have it show zero items in cart. I use zencart, but don't know a lot about it (that's why I have a webmaster!) Webmaster doesn't see it as a zencart issue, but with it happening with multiple customers in the US, outside the US...ideas/suggestions anyone?

[DrByte]

Error started happening a couple o of days ago

Okay, what "changed" "a couple days ago"? including server software updates? server "security settings/headers" changes?

Most customers not able to log in.

You didn't say what it "looks like" when they "can't log in".
If it's a password failure then it will say "sorry" in some way.
If the password is valid then no error will display, but if the system can't start a "session" and set a session cookie to the customer's browser, then the customer won't have any indication of being "logged in".

tried putting things in their cart, only to have it show zero items in cart

This typically means a session didn't start and/or the session cookie couldn't be set/read.

Session problems can be caused by a dozen technical reasons. The most common include:
- out of disk space in your account's storage quota for either the filesystem or the database, or both
- unwritable directories where session data might be getting stored
- overzealous security rules in the domain configuration in the server's vhost
- cookie domain doesn't match website domain
... and lots of other things that are usually more associated with "new" sites that haven't "already been working" yet