4I

Were you surprised when Chastain brought up Eleanor Wish? Would this be a problem for Bosch?

Not surprised, he wants to get Bosch and knows a lot. Bosch seeing a known felon who he interviewed in the case is a serious matter that could cost him his badge.

Chastain seems to be trying to cause trouble for Bosch. Eleanor was at his house during his off hours.

While he's not allowed to be around a felon, it's a slap on the wrist compared to what else he's being accused of. He just wanted to get under Harry's skin.

Chastain always gets his man (or woman…). If he cannot get him for the planted gun, he can get him for this. His record will not be harmed. But agree with >4 Olivermagnus: his consorting with a felon is not nearly as serious

It's certainly a bit alarming to find that Harry's every move seems to be known to Chastain. Is his house being watched?

Bringing up Eleanor did not surprise me. Bosch will have been very closely watched, considering the suspicions about him.
Consorting with a known felon will be a problem for him, but a minor one considering the other charges hanging over him.