Invoice Number not sequential

We have already seen a few threads mentioning that the issue was because there were cancelled or refunded orders that were taking up numbers but we didnt have any cancelled or refunded orders.

Are there any known issues why your plugin skips invoice numbers and is there a fix in place or something to try?

If you have set the ‘Display invoice number’ setting ‘Invoice Number’ (‘Order Number’ could also cause gaps, see: Why is the PDF invoice number different from the WooCommerce order number?):

And you indeed have no cancelled/refunded or deleted orders, then there are only a few possibilities left:

1. The ‘missing’ invoice numbers are assigned to (much) older orders
2. There is a so called ‘race condition’ affecting your setup. This is mostly caused by payment providers, a well known example is for PayPal: if you have setup PayPal with payment confirmation by both IPN and PDT, PayPal will send duplicate/concurrent confirmations, resulting in emails being sent twice, stock being reduced twice… and invoices being created twice (only 1 survives).

Can you confirm any of the above?