I have had the same issue with the ACK bug ever since v3. If a device goes down and you acknowledge it, then it comes back up, then it goes down again it will show acknowledged as soon as it goes down. It should show red whenever a device goes from up to down even if you have previously acknowledged it. It is obvious to me that this is how it SHOULD work. This SHOULD be considered a bug, but at this point I'm starting to think that this is how Mikrotik intends it to work. This bug has been reported several times and has existed now for 2 versions. This should be an easy bug for them to fix, but they seemingly refuse to. Or maybe they are still just unaware. Haha maybe Mikrotik just never has any devices go down at their office so they have never seen this bug.
I'm also having other problems in v4b3. It seems like several of the built in probes don't work properly. The memory probe has been especially troublesome. It basically won't work on any of my Mikrotik devices. I just consider it broken. The disk probe has been unstable as well. It randomly shows down. Today the CPU probe has also started randomly showing down. Basically the only probe that is reliable is the ping probe. If the ping probe ever stops working the Dude will be 100% useless to me.
I love the Dude, but I'm about fed up with it because it's starting to seem like it's being abandoned by Mikrotik. I wish they would devote more development time to it. It could seriously be a valuable tool. I know v4 is still in beta, but I feel like I have to complain because if these problems go unnoticed they will exist all throughout v4 like the v3/v4 ACK bug. I'm anxious to use some of the new features in v4. I hope you guys can figure out how to get these problems fixed!