Larger part won't print properly

[Lez0]

Hi all
I'm having a frustrating time with some very small parts I'm printing on my Saturn 2
I did a teat print of the collet and it printed fine. This has a 0.5mm blind hole in the middle.
Then I added a thread handle etc. and printed it, the 0.5mm hole is blocked.
I've checked the part in Chitubox and it shows the hole in the middle.
I've tried various changes but the hole is allows blocked, I even tried printing 3 collets together and they turned out perfect.
So can anybody tell me why the larger print fills the 0.5mm hole in.

collet on the left body on the right.

Thank you

[Lez0]

Well I think I know why these haven't printed, the resin. As I've been printing a lot of very small parts I haven't needed to top up the tank with resin, so it's been in the tank a while, getting dust etc.
I did a very large print and had to top up the tank, I noticed that the resin in the tank was darker than the new resin (white).
After the large print was finished I printed the larger of the 2 parts above and ,hey presto, it had a hole in it.
I can't explain why the smaller parts printed OK, but I know what the problem was.
Lez

[Scott.H]

Thank you for the info. I've often wondered about this.

[Lez0]

I also found that if I print small slots (0.3mm) they print a lot better if they are horizontal to the plate instead of vertical.
Vertical it can be 50% or more failure, horizontal it's about 5% failure.
I don't know why because everything else is the same.
Lez