No data in invoice number column

UPDATE
I notice that if I disable the option “enable invoice number column in the order list” the problem seems to disappear; invoices numbers are the same of orders numbers.

I noticed also that in two orders, happened with one minute of difference, the invoice numbers have reversed (order #16 happened at time 17:35 created invoice time 18:05 with number #17 – order #17 happened at time 17:36 created invoice time 17:57 with number #16).
What it could be the problem? Can you help me, please?

Hi! Invoice numbers are entirely separate from order numbers, for good reasons. An invoice number is not created until an invoice is created, and if you create an invoice for an older order after a newer order, the older order will have the highest number. Much more detail about this (and how to resolve this if you really want them to match the order number): Invoice numbers explained.
Note that sequential order numbers does not guarantee sequential invoice numbers! This is also explained in that article.

Hope that helps!
Ewout

Thank for your answer, I check better the link you gave me.
I don’t understand 2 things:
1- Why when I disable the option “enable invoice number column in the order list” the problem seems to disappear?
2- Why some invoice takes 1 or 2 minutes and others also some hours?
Thank you very much for the attention and the help

1) Correct me if I’m wrong, but I think this is purely cosmetic. If you disable the invoice number column it only shows the order number and the invoice number is not shown at all.
2) This depends on the payment method used. The invoice is generated as soon as the email is sent.

Hi, thanks for the answer, but I assure you that if I enable that option the invoice number in the column sometimes appear, sometimes not appear and mess with numerations of the invoice ( like I descibed in the first post).
For the payment method I use only Paypal and (I don’t know if it would be helpful to you) in the attachment option I enabled “Email customer complete order” “Email new admin order” and “Email customer invoice”
Thanks again for the attention

Hi! Showing the invoice number has no effect on whether it’s generated or not.
The ‘numerations mess’ is simply a result from the order in which the invoices were generated (either by the admin clicking the button or the pdf from being sent by email). You can easily verify this by placing some test orders.
Paypal can have a small delay in the payment processing, which could explain the difference in invoice number order.

Again, the order number and invoice number are entirely separated for good reasons explained in the documentation I linked to.

I would recommend against attaching the email to the admin new order email because that also generates invoice numbers for orders that are never paid for, which you will probably want to avoid.

Hope that helps!
Ewout

I wanted first of all to thank you for your help and patience, I think I understand what you mean.
I want to ask one more thing: I first received an order that was subsequently canceled by the customer and after another two orders, to the canceled order, the invoice number was #38, the other two subsequent orders (not deleted), #36 and #37; It may depend on the setting “admin new order email” or it may be something else?
Thank you very much again

Indeed, if you want to prevent invoice numbers from being generated for orders that may still be cancelled, you should disable the attachment to the admin new order email. This email is sent immediately, as soon as the order is placed when it still may be cancelled. The ‘processing’ status usually means that the payment has been received, so processing or completed is usually safe.