Blizzard's freeze proc tends to ignore certain enemies (of the same kind) every time, whilst always freezing the others. Definitely a server-side bug. It's too bad because freeze is practically an essential skill to use to CC enemies -- especially as an sniper. As you can see I am having trouble keeping enemies at bay because they are not being frozen in place. I have seen other threads about this, however no solid solution has been found.
This used to happen to me and friends of mine playing as White Knights years ago. It was related to the compatibility mode, and running the client with compatibility mode Windows 7 did the trick, making freeze debuffs work as intended. We were running Windows 10 as OS. However, I don't know if this is relevant today, what with all the custom client edits that have been made since, but perhaps give it a try!
Unfortunately, I use Linux with MapleRoyals running on WINE. Fortunately, WINE can be configured to use multiple versions of Windows both with 32-bit and 64-bit architecture. Unfortunately, I've tried every 32-bit + Windows version combination and version Windows 10/7/XP/98 + 64-bit, and nothing works. I guess I'm just stuck with this?
I just did some quick testing with both the WZ and IMG setups. Without windows 7 compatibility enabled, the freeze for blizzard does not work. With Windows 7 compatibility enabled, freeze did work as intended. In general, I don't think we can guarantee that MapleRoyals will work correctly when run on WINE. However, I'll forward to the devs since I ran into this same problem on my windows machine.