The document numbers, which were previously generated normally, are now generated as fractions. For example: Sales Order 1/23. What should I do?

May be, one number was changed by you manually. And all numbers generating ubnormally now. Or may be you used prefix.
If you want to correct this situation, you should renumber documents. And next documents will number correctly.

Wow! It's fine now! Thank you, Mikhail!