Hi Dolorm. 
Thanks for your question! There is an issue with Solana’s API that started happening yesterday.
The team is aware of it and are working on a fix as we speak. 
There is also a 503 error that is happening so if you see this one also, I can assure you that they are working on both of them. I don’t have an ETA but I’d advise trying to sync your wallet later today/tomorrow to see if it’s fixed.
I’ll do my best to keep this thread updated too. 
The alternative is that you could try and grab a CSV from https://stake.tax, but if you can I’d advise waiting for the API issues to be resolved.