How to stop these startup entries from popping-up every 3-4 days

Check in Task manager > Startup and disable "Macrium Reflect UI Watcher" and see what happens.
There are also these services:

One of them is to enable MR to mount .mrimg files, just don't remember now which one exactly.

Sorry, I don't use Cleaner so cant duplicate that but maybe Download Microsoft Autoruns - MajorGeeks can find exactly what is running in that case,

You are probably correct that you see them only when Reflect schedules them to run after the next restart/boot-up. I don't see either of those tasks on my PCs running Macrium Reflect. I see only one entry for Reflect UI as shown here:

HTH,
--Ed--

Maybe it's an update checker. Disable it in Macrium

Ooooh! Good call, @AndreTen. I bet that's it!
--Ed--

EdTittel said:

Ooooh! Good call, @AndreTen. I bet that's it!
--Ed--

We'll see :)

Since that, I have 2 new entries shown in CCleaner as startup items /see screenshot bellow/. What they are suppose to mean and how could I remove them permanently? When I delete them, they come back in few days. I normally make only one full backup and don't need any scheduling or incremental / differential ones.

Short answer: download WhatInStartup - Disable/delete programs at Windows startup
run as Admin and delete these 2 entries from startup, you don't need it.

Long answer: After installed Macrium. At startup, there will be 3 background processes running as shown:


Normally, you'd have one entry in the startup as shown above by @EdTittel and I always delete this entry until Macrium runs upgrade then it will put back in the startup.
I suspect when installed Macrium, you used different user name.
Macrium Reflect UI Watcher


NOTE: Cannot disable or set to Manual the Macrium Service. If you disable, the next run it will re-enable and set back to Automatic. Will break if you delete this service.

topguntcp, if one installs MR6 or MR7 for all users, would it still matter which admin acct was used?
I'd like to learn more from you :)