All notes from "Notes" app have been deleted for no reason!

Check the Recently Deleted folder. If not there, you can restore the iPhone to a backup that was made when the Notes were on it.

As I said before, trying to determine why they vanished is probably not going to happen at this point. Things happen sometimes and we won't always find a reason. What you really want is to recover the notes and that is what we are trying to do. If these email accounts have Notes turned on, then they would all appear on your phone, and in the same place, Notes. What I've been trying to get you to figure out is if they exist in one of your email accounts. You need to log into your individual email accounts on a computer, using a browser, and then find their Notes tab. As far as backups are concerned, are you using iCloud? If so, you will only see a couple of backups before they are overwritten. To see how many backups you have if you are using iCloud, go to Settings><yourname>iCloud. Under the Storage graphic, you see Manage Storage, tap on that. On the next page, tap on Backups. That will show you how many backups you have.

If Notes appear in any of your email accounts, we can work from there, but if you have done a backup since the Notes were deleted then restoring them if they don't exist anywhere else probably won't be possible, because the backups have been written over with new ones.

So you do not use any of your email accounts for Notes, and do not use iCloud. Then you need to restore the device to a backup that was made before you lost the Notes.

Can you look in Settings>Passwords & Accounts, and see if your email account has Notes listed in there. If so, that means that notes are turned on for that account. You need to go to that email account in a web browser and see if your notes are there. If notes are turned on for that account, then those notes would be there and on your phone. It is possible that got turned off for some reason.

You don't have a backup of the iPhone? You just said the Notes were not in a previous backup, in your last post. If you don't have a backup, of course you cannot restore them. Without a backup, you are out of luck. While it would be a mystery as to why that happened, without a backup, there is no way to restore any lost data.

I cannot explain why they disappeared either, however your only chance at restoring any data is a backup. If data is important to you, then start making regular backups. iCloud provides you the opportunity to set up backups once, and it will do an automatic daily backup if you connect it to power, wi-fi and lock the screen. This happens when I plug my phone in to charge every night when I go to bed and I have a daily backup when I get up in the morning. The most data I can lose is what I've done the day from the time I get up until I go to bed.

I depend on my Notes app on my iPhone too and use it at least three times a day. Every once in a while the contents disappear but the list of notes is visible. This is definitely a glitch with the software. I have an 8 plus and it is up to date. I usually have to power off completely, wait a few seconds and then power back on again and everything is there. I hope Apple is aware of this issue and can fix it for us.

There obviously has to be a language barrier here. I did not ask you to check iCloud, I asked you to check your email account that has Notes turned on for it. You told me that you had an email account that had Notes turned on. That is the one I want you to check. It has nothing to do with iCloud. If you have an email account that also allows you to sync notes, go the web access site for that email account and check to see if your Notes are there. If you created a backup of your phone before your Notes were lost, then you can restore to that backup. If you have backed up since you lost the Notes, then you cannot restore to the backup, because it would have been written over. I hope you understand what I've asked you this time.

So let me see if I understand you correctly. You restored the iPhone to a previous backup made before the Notes disappeared, and the Notes were not restored? Are you sure the backup you used was from before the Notes disappeared, or had they maybe disappeared before you realized it?

Are you using On My iPhone for Notes, or iCloud. If iCloud, it could be a connection issue temporarily with iCloud sync that could cause the issue. I cannot be sure of that, but since using iCloud to store the content and syncing to the iPhone, a temporary disconnect with the internet could cause an issue between syncing the content in iCloud to the iPhone.

I’ve checked all that. They were saved on my iPhone not iCloud and I’ve gone and checked all my email accounts. That won’t do anything if they are saved to my iPhone.

I furthermore checked and if I search for a note that was saved on my phone I can find it but it won’t open it so they are still on my iPhone but for some reason just not showing up in my notes!

I’ve checked and I don’t know if my email address has notes. I’ve checked and all my emails in settings have notes checked and still no notes showing up that were stored on my iPhone. Now when I go to search for them they aren’t showing up in my search. So annoying. I went to look for a backup to see about restoring to a backup that had notes on it previously but it’s only showing one backup that was done this morning. Now I don’t know where previous backups are on my phone!

Comes down to why notes that were stored on my iPhone have just vanished.