Has anyone been able to buy commercial brewer's invert syrup and compare it to what they made?
AFAIK, even in the UK it is only available in industrial quantities, such that even smaller craft brewers are SOL. Hence the interest in making it at home. On a related note, brewers caramel, aka class III or ammonia caramel, is not only unavailable to homebrewers but impossible to make for yourself. Making true to style British beers is a challenge.
If you got stratification or crystallization, it didn't fully invert; not enough time at sufficient temperature. If you get a consistency like jelly instead of pancake syrup, the temperature went too high. Even a brief instant spiking too high will take the candy making process to the next stage, irreversibly.