Multiple Google Merchant Errors with Online Store & Shopify

Google has recently sent us several emails informing us 'Google Merchant Center Alert: Drop in Number of Active Items for Gartrac'.

We were advised to install Simprosys but not sure why as this hasn't fixed anything.

We have errors:
- Missing Shipping info in some countries
- Mismatched currency in shipping information
- Missing local inventory data
- Invalid GTIN Value
- Image too small for upcoming enforcement

I have tried to fix the Mismatched currency in shipping information in the google merchant centre and in the 1st instance it worked but I refreshed shopify and it overwrote all of the data and changed it all back to the Country local currency when we need it to be GBP. There must be a high level code somewhere that stops this overwrite.?? I have been trying again today but I expect when I change something in shopify it will oversrite it again to show EURO or USD instead of GBP for all shipping rates.

Image sizes - we can resolve with new photos

Invalid GTIN Value - we don't use bar codes, so I can change each part to go by SKU instead.

Missing Shipping info in some countries - we don't want to sell to some countries and I took out the shipping rates and now this error appears!

Missing local inventory data ?? Is this because we set up having a local store ??

Can someone who knows what they are doing with these errors please quote to resolve.

We sell globally and shopify is set up to sell to customers in their own currency, but I am not sure if the google merchant centre likes this?

The fix ISN'T too remove all of our products from countries in google merchant, which then looks like error is resolved. Or to remove our local store.

Can you please quote, including the process you plan to resolve these errors and get our site and up and running as our online sales have been impacted. And any examples you have resolved simialr issues with other customers.