repository for ubuntu/linux mint for R 4.0.0

In updating (an older computer with) Linux Mint 18.3 I tried to add
the repository

deb https://cloud.r-project.org/bin/linux/ubuntu xenial-cran40/

as per the "Download R for Linux" instructions. This gave an error
that there was no Release.key file.

After some investigation, I found that

deb https://cran.r-project.org/bin/linux/ubuntu xenial-cran40/

i.e., CRAN not CLOUD. With this change, I could install R 4.0.

Is this a known glitch?

Dear JN,

perhaps it is a glitch ... does anyone run mirmon[1] on the R 
mirrors to see which ones are old?

If you open those two addresses in a browser, you see that the 
xenial-cran40 folder is only present in cran case ...  These are 
two different servers, which can also be seen by running curl:

	rasmus at twentyfive ~ % curl -I https://cloud.r-project.org/bin/linux/ubuntu/
	HTTP/2 200 
	content-type: text/html;charset=ISO-8859-1
	date: Thu, 30 Apr 2020 00:05:13 GMT
	server: Apache/2.4.39 (Unix)
	cache-control: max-age=1800
	expires: Thu, 30 Apr 2020 00:35:13 GMT
	x-cache: Miss from cloudfront
	...
	
	rasmus at twentyfive ~ % curl -I https://cran.r-project.org/bin/linux/ubuntu/
	HTTP/1.1 200 OK
	Date: Thu, 30 Apr 2020 00:05:23 GMT
	Server: Apache
	Content-Type: text/html;charset=UTF-8

It is wise to point your package manager to a mirror[2] close to you 
instead of a cdn, e.g. [3] or something ... 

Best,
Rasmus

[1] https://spacehopper.org/mirmon/
[2] https://cran.r-project.org/mirrors.html
[3] https://mirror.las.iastate.edu/CRAN/bin/linux/ubuntu/