Can't boot OS

[Logman]

So I thought I'd try again to set up unlimited primaries, same result

The Nvme drive (500GB) is set up as follows:

Win10= 126GB,

Free Space= 136GB

Ubuntu 18.04 = 105 GB

Mint 19.3 = 105 GB

Free Space = 28GB ( reserved for over-provisioning )

BIBM = 6.3 MB

I want to set Unlimited Primaries as I currently have 4 Partitions.

I first resize the Ubuntu Partition to 70GB using Gparted as per TeraByte knowledge base article, then move the Partition to the end of free space so it's adjacent to the Mint Partition.
That leaves me with 171 GB of free space between Win 10 and Ubuntu.

I want to split that free space into 2 partitions so I change to Unlimited Primaries, and create the 2 partitions.

So now I have 6 Partitions which is what I want so I can put Ubuntu 20 and Mint 20 on those 2 partitions.

Everything seems fine for a couple of days until suddenly I can't boot into the original Ubuntu 18.5 partition again, just get the white flashing cursor on top left of screen.

Seems like the only way to get it back is to redo the whole setup again back to Limited Primaries.

Anybody have any idea what is going on ?

[Logman]

So it's been a month since I decided to just leave that 105GB Ubuntu partition as is, and changed to Unlimited primaries.
I ended up creating 2 partitions of 68GB between Win10 and Ubuntu 18.04.5
Installed Mint 20 and Ubuntu 20 and everything has been fine since then.
I guess for some reason there is some kind of bug when resizing an existing Linux partition smaller.
I did the same with Win10 ages ago and there was no problem at all.
I upgraded Win10 to the 2004 version last week and was happy to see everything was fine with BIBM, nothing changed at all, and all 5 OS's boot normally, so that was a relief !