Hey
ABACABB, what this means is that your shatters are being predictable to higher skilled players. What this means is that you need to practice new shatter mixups, usually the best thing to do this is to make the opponent scared to jump. This is usually best achieved by holding a hail above your head so your opponent will be wary of it and not want to jump into it. I advise you to use hail as much as possible since it's Glacius best tool in my opinion and will improve your Glacius in every match-up.
Let me give you some shatter mixup examples. If you do a far shatter and the opponent jumps forward what do you do? You actually have a couple of options you can try to tripguard the jump with icelance into medium shatter, or just raw medium shatter, or icelance into hail if you think they'll jump after your icelance, or summon a hail into medium shatter.
If you end your knockdowns with the qcb-p ender you have enough time to set up a hail I'm sure you know of this setup. This way you have many mix-ups as glacius, raw shatter on wake up, HP into shatter as you release hail (the shatter will actually hit first), or release hail jump overhead light kick, or release hail jump cross up low kick. or just walk and grab. If you catch a player counter breaking a specific string, you can cancel that string into shatter and it will punish them.
About long range combos, usually good players can break heavy and medium autos on reaction. It's just about how much you can risk, or how you good you can bluff. If you always start your shatter combos with light auto doubles into shatter this is very hard to react to so if you catch a player again with shatter they might guess lights, this is where you can assume they'll guess lights (to get a lockout for a long combo) or counter break (for a heavy damage combo). it's really about the habit of players. Some players try to break everything they can react to, others almost never break a long range combo to bait the counter breaker.
Best advice is try to add a good Glacius player (I think CVE Rivz is one of the best right now) and just learn from their setups, record the matches if possible and look back and see what setups worked and practice them.
Maybe you can play vs me and tell me what could I improve 
?