Gary, Mike, et al;
This has been a problem for many folks. Gary, how much free space in GB do you have on your C: drive from that screenshot? MS does a thing that if you have less than 25% free space remaining on your C: drive, it will automatically delete Restore Points one at a time until it reaches the 25% free space size. This excludes the 22.51GB (5%) you show on your screenshot. This means that if your C: drive has 76% used, that the free space is at 24%, below the threshold and you must then subtract the 22.51GB from that 24% figure (on a 250GB drive say, 224GB usuable, where 24% free space is 53.76GB), then you subtract the reserved amount from that (53.76GB - 22.51GB = 31.25GB). Free space on the C: drive then drops to 14.20%,
WELL BELOW THE 25% THRESHOLD; so on a smaller hard drive,
this example would cause Windows to start deleting Restore Points, since it's below that 25% free space threshold. 
[This next paragraph also deals with holdum's example from his screenshot.] The other thing I know about Restore Points is that Windows cannot store any Restore Points going back more than 5 months previous to your most current Restore Point! This means that if you have one set today, May 11th 2016, all Restore Points on your C: drive prior to 5 months ago (Dec. 11th 2015) get automatically deleted by Windows!
A lot of people are not aware of this. In your example screenshot from
POST #5, you only go back 5 days, and you have the
SHOW MORE RESTORE POINTS checked, so that's indeed odd. Are you sure that you didn't disable your
SYSTEM RESTORE by disabling it manually around 10 days before (prior to 4/19/16)?? And then re-enabling it right around 4/19/16 where the first Restore Point is shown? If you're sure you didn't do that, then you need to check your total drive useable capacity against the free space and deduct the 5% Restore Point reservation figure and do the math to make certain you haven't violated the 25% free space threshold. If you do this and you've got somewhere between 30%-50% like I said, and you didn't manual disable the
SYSTEM RESTORE option under the
CONFIGURE button, the magically disappearing Restore Points are not coming from within Windows itself.
What also just occurred to me, is that I'm aware of certain viruses that go after
SYSTEM RESTORE, and randomly delete all your Restore Points, one at a time.
If you don't find and remove that virus, eventually you'll be left without the ability to general Restore Points using the Windows built-in program.
You could use the
Restore Point Creator program Mike suggests (am still trying that out), but don't know whether the virus would affect that program as well.
It might be worth it to rescan your W10 system again using your built-in AV, and MBAM, and also check for RootKits and Bootkits using TrendMicro tools. I run into this problem quite a bit with Client machines, and sometimes virus scanning and repair will find and delete these little nasties. And sometimes not. Intuitively, when I find a machine like yours and Mike's where there are only a couple of Restore Points left, and it's one I repaired say a year ago, so I know for a fact I always turn on System Restore, then I attempt to resolve that problem by running the virus scan process. If I see the machine in a few more weeks or months, and I see Restore points once again disappearing, it's likely that it could be a new mutated version of the viruses that attack System Restore and there's no antidote currently available
*at least for a few days or weeks until the AV guys find it push out the antidote in their regular udpates*. At that point, I usually make the decision to do a Windows Reset or Reinstallation from factory Recovery Media or Partition and do a hard drive wipe; not just the OS partition, but the whole hard drive!
This always seems to work, except for the rare occasion where I forgot to test the hard drive prior to the Reset/Reinstallation, and the drive itself is faulty.
I may know a thing or two more about this process than the average tech, as I was a Beta Tester for the old
"GO-BACK" product in W95 & W98, which used to be a separate retail product that you could install on your PC to rollback your system if you damaged your windows or caught a virus, installed a bad driver, etc. The
GO-BACK technology was originally purchased by Microsoft and is now called
SYSTEM RESTORE. MS made a few changes to it over the last 20 years, but, it basically works the same now in W10, W8X, W7x, Vista, XP, etc. as it did then. You guys are old enough to probably remember this product and it's incorporation into Windows.
So, if your machines meet the limiting guidelines I outline above, and you check thoroughly for viruses (remember to Bootime Scan if you can!); and your Restore Points keep disappearing, something is awry with your W10 (or any version of Windows for that matter) and it needs to be repaired. [easier said than done
.].
Cheers!
<BBJ> 
I like the simple interface so far.
I do like the program and User interface BTW.
