I am having this same exact issue. I had a chat with Shopify this evening and they mentioned they have made a change but that’s related to GTM.
Pasting the chatlog below -
14:08 Ace C (Support Advisor): I do apologize, but I am well aware of the situation. sometimes, the thank_you url is firing, sometimes it’s not. The reason being is an update because people were finding a loophole to use GTM on non-plus plans.
14:09 Ace C (Support Advisor): now, it was randomized in a way that will still fire with Shopify Analytics for conversion, which is recommended, but can still work with Google Analytics.
Also, with regards to the Google Pixels not firing -
14:13 Ace C (Support Advisor): I think this has something to do with UA sunsettng and being replaced with GA. Also, support for this is now deferred to google as they took over support for all google apps within Shopify. you can actually go to your admin>apps and sales channels>Google and youtube channel>Get support
14:13 Ace C (Support Advisor): because even with our changes to the thank you URL, GA should still be able to track conversions
14:13 Rishika Namdev: Exactly
14:13 Ace C (Support Advisor): I would encourage you to contact the Google and youtube Sales channel support
14:17 Rishika Namdev: I am using super basic integrations so I am 100% sure something is broken here and not just now since about a month
14:18 Ace C (Support Advisor): I understand. that is why I’m asking you to contact the sales channel support. They can definitely help you out with this Rishika. We are able to detect issues on our end. but they’re more trained technically
If anyone has found a solution, please let me know as well. Its been over a month now.