This is an issue caused by how the payment form has been coded by the web developer for the site you are visiting. For example, many payment forms do not label or activate the expiration date input fields until after you have manually placed the cursor into the card number field and started typing.
The only solution would be to build a very large database of heuristics to try on each payment form (rules for identifying expiration date fields and methods for circumventing website controls that prevent those fields from being filled), but this would invariably cause the autofilling to be delayed, and likely also cause false positives (filling of expiration date data into fields that are not meant for that purpose).
If you have a few payment forms that you use frequently, then you may be able to use custom fields to solve the autofilling problems, but this is not a scalable approach (for the same reason that having Bitwarden build a list of custom rules would not be scalable).
I’ve found that a work-around that solves autofill problems on many payment forms is to autofill once, then click into the card number field (or for stubborn cases, click into all input fields), and then autofill again. This process can be completed fairly quickly using the new keyboard shortcut for autofilling card data — which must be defined by the user (I use Ctrl+$ 
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