How to completely disable Gmail categories and see all messages in inbox?

Question

I would like to configure Gmail to behave like a traditional email service where my incoming messages all appear in my inbox by default. I don't want them sorted into "social", "updates", "forums", and "promotions" categories. I don't mind if Gmail wants to discreetly do that in addition, so long as I will definitely see all my messages when I go to my inbox.

Unfortunately I do not seem to be able to achieve that behaviour, and Gmail behaves very inconsistently. I've already disabled categories in the settings:

That has resulted in the removal of category tabs at the top of the page and what appears on the surface to be a unified inbox view. However, I can still see the categories on the left-side menu:

That would be fine, except that I'm observing the following inconsistent behaviour:

1. Messages will sometimes appear in my inbox but not a category
2. Messages will sometimes appear in a category but not my inbox
3. Messages will sometimes appear in my inbox and a category.

Often the above messages will be very similar looking ones from the same sender, making the behaviour seem almost random. When I click on "all mail" it appears that some messages are being tagged with an "inbox" label while others are not:

My Google searches reveal that this is a common problem but not one that I've been able to find any solution for. For example, see here and note how heavily downvoted the answers are which claim that disabling categories in the settings is a solution.

What do I need to do to have a 100% guarantee that I will see all non-spam messages when I click on my inbox in Gmail?

Answer 1

Shortly after I posted my question, I found the solution in point number 4 on the answer on this page:

Hi Stacey, there are four places that the Inbox label can be removed.

1 - [...]

4 - If another device (e.g. mobile phone) is connected to your account using IMAP, archiving messages in that device will remove them from your Inbox.

After some experimenting, I've discovered that the Android Gmail app is configured to "archive" rather than delete your emails when you swipe left or right. Archiving an email causes the inbox label to be removed but leaves a copy in the categories (if any) and otherwise removes it everywhere except "all mail". The fix is to change the settings in the Android app:

3 dots menu -> Settings -> General settings -> Swipe actions -> Change "Right swipe" and/or "Left swipe" to the "Delete" action