Thank you very much for your reply.
I thought the previous issues had disappeared not the error. Sorry for miss understanding.
Well, it makes perfect sense that error related to WC 3.5.1 had disappeared as ATUM is not compatible with 3.5.1. It was only released yesterday. We would not have any time to test new WC release with ATUM. Testing will take some time and we will release an updated version as soon as we finish.
Please, remember, you should not upgrade any of your main site parts unless you test them in staging site. follow change logs and only use plugins that stay supported.