If you only use silver coins, the exchange rate shouldn't change.
To solve your problem, the programmer first needs to replicate your bug. Could you please upload your game save file to our dedicated page: https://nonohom0-circle.notion.site/Bug-c7dd050b559544c6b03e47d2cf96524c?pvs=4
The cache path for Unity PC saves is located at: C:\Users<user>\AppData\LocalLow<company name>
The cache path for Unity Android saves is located at: /storage/emulated/<userid>/Android/data/<packagename>/files
Please don't forget to modify your file name or write down the bug on our page so that we can distinguish these files.