Big problem with google traffic since 4 month after switching to OpenCart. Please help.

We had a zen cart shop and a blog. Zen cart brought most of the traffic, the blog just a little bit.

Zen cart is a real work horse but since open cart has a more modern look and some other feature, we decided to switch to open cart. We also changed from http to https.

Maybe two weeks later after we switched to Open Card we had a HUGE traffic drop. Maybe 60-70% loss. We hoped it would go up again but this has not happened. It has been 4 months.

What I see. The blog has now most of the google traffic. The shop hardly creates any direct hits from google. It has been reversed as it was before.

Any advice? We have SEO friendly links in the shop.

Nobody any advice?

Also, we export a sitemap via opencart. The sitemap has nearly 300 items but google has indexed only 90 after 4 months.

I just saw at google search console that Open Card does put a lot of "canonical tags" where there should be no "canonical tags". Also, google console has a lot of shop pages: "Indexed, not submitted in sitemap" This does not sound good. The build in XML Sitemap seems to be utterly broken. Can somebody recommend a decent xml sitemap plug-in?

There's one in my signature below