what's happening is you are getting an invoice in USD for your CAD subsidiary. You are putting that in at a particular exchange rate. This is stored in Netsuite at the CAD amount. Then, when you are running your report, it is translating this CAD amount live to the USD (consolidated) amount using the consolidated exchange rate for the period (it's not clear whether your report is on balance sheet, which would be current, or P&L, which would be average - probably it's a mix). This rate is almost certainly different to the exchange rate of the transaction, hence the difference
For any item that hits the balance sheet, then you'll get "moving" results. When you specify the criteria of the search, Netsuite will take a guess at the consolidated exchange rate to use for the whole report (I think this is based on the last period it can find entries for) and convert everything at that rate, mirroring how consolidation works. The effect of this is that the same transaction will have a different amount when you run it with the context of Jan 2022 compared to Feb 2022.