They are:
Stale: you sent the share after the block changed
Dup: you sent the same share twice (this isn't really that uncommon)
Hi: the pool wanted Diff X shares, but you sent Diff Y shares (where Y is less than X)
Rej: there was something wrong with your data you sent to the pool. An example would be: you pointed an LTC miner at the pool
HW errors aren't part of any of that coz the miner doesn't send them to the pool.
Got it. Of my miners, only one has any issue with Invalids. Here is the data associated HI = 46,302/3. Every other miner has 0 across the board. Remedies, is there anything I can do improve performance? Thanks.