Trying to search for a member by either email or member ID in the ACP doesn't return results. Is this a known bug that's being fixed?

In the new version of IPS spoiled the ACP's research.
All that matters is speed! User need not matter.

Summing up. The IPS polls that were no longer good, are getting worse every day.

Another change I didn’t like is the member field (or even the ACP search): before you could search for any piece of the member name. You can’t do it now. 

Example: doe used to return John Doe and anything starting with doe. Now you need to type john to get a list of users starting with john and probably will have to type doe to get to the right user.

Yes! They took the like %search% 

Here I had to make several customizations at the core of the IPS to make the search better.

#1 The change you're talking about wouldn't have anything to do with member ID

#2 We have already changed the behavior so that %string% is used if you have less than 1M member records

	/**
	 * @brief	Cutoff to start doing LIKE 'string%' instead of LIKE '%string%'
	 */
	protected $inlineSearchCutoff	= 1000000;

So....those posts are not factually accurate at this time, and I would encourage the OP to submit a ticket if you're having trouble with live searches.