E-Mail forwarding not working for some senders

[neufuse Veteran]

I am suddenly having issues with e-mail forwarding, this has worked great for years then in the past few months I don't get all my e-mail.

What I have is my ISP e-mail account which has spam filtering turned off completely. Then I have a  custom domain that I purchased years ago which is currently hosted via google domains (yes I am aware it's transitioning to squarespace, ironically this issue started about the time of the sale completion)

So two examples, I have an account with walmart.com which I always was able to get emails from, then suddenly nothing, no order notices nothing, then I also have an account with slickdeals.net which sends a bunch of emails a day to me, got them fine in the past with this e-mail forward. Then out of no where nothing from these two sites.

I made a new account on both sites using my ISP e-mail directly and I receive the e-mails fine from there, so it's not the ISP email, it has to be something to do with forwarding?

I get e-mails from a lot of other sites just fine on the forwarded e-mail address, so it's not like it's a MX issue, SPF DKIM all the other records are correct not that it would be an issue with this.

So the setup:

I have an e-mail with my ISP, which works correctly, it receives e-mail fine from the domains that this isn't working with.

I have a domain forwarder with my google domain account that forwards e-mail from my custom domain to my ISP email. When these domains send to this email address I never get them.

 

So why would I suddenly stop getting e-mails from a couple sites and not be able to from them to the forwarded address domain? Even if I make new addresses on that domain with the forwarder and make new accounts with it on these sites, the e-mails still never show up when using that domain.

The domain doesn't appear on any blacklists that I've checked. There also is no SPAM or filtering settings available for the domain on the forwarding side.

To see if it was the forwarder, I ditched that and converted it to a google workplace account for that domain and set it up with Google email services... and I still get nothing from these specific sites using that domain.... I'm stumped

Any ideas?