Turns out the Tactics Ogre iso I got had the same problem too. It just took longer to manifest... Ugh
What are the filesized when ISO and CSO? Your memory stick may have a read issue and by compressing it as CSO you trimmed it small enough to avoit the issue (whether it's certain sectors or sequential read time in general).
It was 28.1mb as ISO then 21.8mb as CSO.
It had a problem when compressing too, I had to change an Lba position (I don't even know what that is, but I changed it. Wouldn't let me compress it otherwise). I don't think it's related to that though, because I tested a new ISO with that same Lba change (just to be sure) and still got the problem.
I remembered something: It happens with music files(mp3) too, the songs skip for half a second and sometimes they just show up as corrupted data. I forgot about that since I dont listen to music much.
It really must be a read issue like you say
You're going to need to do a MS speed test....a PSXReality memory stick test would be a nice result for you to post.
Total Space 3999268864 bytes ClusterSize 32768
100 0.029966 0.000528 0.114187 0.000165
1024 0.515680 0.066299 1.301935 0.003264
2048 1.112030 0.088397 2.226170 0.003952
4096 1.932045 0.367629 3.446920 0.009132
8192 2.845342 0.386486 3.932796 0.011294
16384 3.260640 0.467005 4.197688 0.001448
32768 3.564873 0.493842 4.367292 0.000887
65536 3.696261 0.513146 4.458526 0.000790
131072 3.243506 0.261804 4.513898 0.000621
262144 3.137487 0.133118 4.540643 0.000446
524288 3.230425 0.240638 4.546332 0.000393
1048576 3.175312 0.166872 4.546475 0.000369
2097152 3.127859 0.127924 4.552477 0.000578
4194304 3.296652 0.128789 4.546541 0.000443
8388608 3.140416 0.158482 4.543454 0.002286
12582912 3.167192 0.182258 5.165407 0.001608
16777216 3.124960 0.090009 5.346958 0.001047
20971520 3.175281 0.111475 5.612359 0.000384
Not sure what to make out of that...