Can I see what changed?

Yes, in the workspace:

• Imports: every import, with what was new, changed and gone.
• Supplier products: each one shows its stock in the supplier's file over the last 30 days as a chart, then every change.
• Store variants: in Store products, each variant shows its stock in Shopify, when a sync last checked it, and every change a sync sent or failed to send.

How far back you can look depends on your plan.