There is nothing wrong with the codes in 'ANY' of the databases. Learning from 1 database to another is going to do nothing, it is the same codes!

The problem is the boxes.

As mentioned, if you get an early production box with the repeat problem, your only recourse is to set the IR to non-repeating and only 1 repeat for transmission.
This makes the remote feel a little sluggish because you can't press and hold to scroll thru menus. And sometimes when you press a button, it doesn't respond (1 out of 10 times maybe).
Or you can return the box and try to get another one.

Exact same issue using MX-450 with brand new 2019 Roku Ultra. Multiple cursor clicks navigating Netflix and Amazon Prime Video only. Since the Ultra remote wasn’t using IR by default, I used an old Roku 3 IR remote to teach the MX-450. Had to do this twice though. I was under the impression that when using an old remote to “teach” the 450 I had to press buttons on the teaching remote for a prolonged duration for the learning remote to “get the message”. When I did this, the problem got worse - one down click to scroll a list registered as 3-4 clicks. I retrained being conscious to click up/down/left/right on the training remote as briefly and quickly as possible. Once that was done, issue solved.

The 450 is problematic. We had this issue with the Ultra and an MX-990 and it was easily fixable because we could adjust the IR send rate. I don't think you can do that with the 450.

I have a TSU9400 and am using the Phillips software. I had the same issue where in Netflix and Amazon the buttons would give a double click.

I set the delay to .15 and that resolved the issue for me. Not sure why but I'm glad it did

Setting it to <.1 and the double click would occur
Setting it to .1 and the double click would occur randomly
Setting it to .3 and the double click would occur