Hello
I have the same question, I can't find in iMessage text, in alfred 3. on MacOS 10.13.4,
when I update MacOS 10.12 to 10.13, alfred search iMessage can't find in iMessage text.
*** Wednesday, May 2, 2018 at 19:59:51 ***
When I update "Security Update 2018-001" https://support.apple.com/en-us/HT201222
I can use alfred search iMessage text.
At 10.13.1 - 10.13.3 can't search.