OneDrive is updating fles... Looking for changes for some 15 mins

Since short I have been experimenting with encrypted files on OneDrive. For this I have been using Cryptomator.
Probably this triggered OneDrive to send me an email titled "Action Required: Signs of ransomware have been detected"
Like this: https://support.microsoft.com/en-us/...7-b8c12c73637f

Likely I am the only one, as the few hits on Internet are my own posts. I went thru the steps on the abovementioned site.

The thing is, at every boot, it takes some 15 minutes from "OneDrive is update files... Looking for changes" to "OneDrive is up to date You are all set".
I have used just about 1/5th of the 1TB that comes with my Office 365 subscription...
If I were to use up the entire 1TB then likely 'Looking for changes' may take an hour or so?

I just wonder, is this normal?
Could this be caused Cryptomator files or would this also happen with any ordinary files (non encrypted)?
In this respect, would there be any difference between BoxCryptor and Cryptomator?

Thanks!

Thanks. Could be, I don't know. The files are within a Cryptomatorvault, physically within I:\OneDrive\CryptoVault.
WIthin that vault there is one folder "\d" with many subfolders, in my case over 36.000 sub folders all containing files with random character and extension .c9r
The vault is password protected and I need to launch Cryptomator and enter the password to make the files show up as normal. Hence my guess is that OneDrive is unable to 'decrypt' it. The modified dates of those c9r files are the same as the 'original' file.

Maybe it isn't a good idea to use Cryptomator after all. Just intended to add a 2nd layer of protection to OneDrive as the first layer (the credentials to log into my PC) I disabled using netplwiz, merely from a convenience point of view.