This error pops up on accounts over 10K transactions. Some of these wallets were synced in the past however refuse to sync now. Even with the start date set. Developers are investigating the reason which is most likely related to the API provider. Workaround I can try using CSV exports from https://stake.tax but I may need to edit the file if I get "Currency not found" errors - I will need to replace the symbols that don't exist in Koinly with placeholder symbols: NULL1, NULL2, NULL3, etc.