A quick search shows that's since the mid 2000s, enanthate has been the overwhelming cause of painful injections. I personally witnessed it from raws I bought that were fine when first used (still powder) and then over a year, caused constant inflammation (had liquefied by this time). I made a mock solution using all the ingredients and left out the enanthate and no pain.
Janoshik confirmed my suspicion years back when he retested some retained samples of enanthate and said it contained multiple decomposition peaks.
There's no doubt in my mind that enanthate is more fragile an ester than cyp or decanoate and just isn't worth the hassle. Decanoate has all the benefits of enanthate with no issues of pain.