Same, announcements are kind of flaky. My usual command is "Alexa, announce <whatever to announce>" - half the time she asks what I want to announce, 20% of the time she announces "announce", 30% of the time it works as expected.
If i'm already on my phone sometimes I'll just type the announcement in the Alexa app instead.
If i'm already on my phone sometimes I'll just type the announcement in the Alexa app instead.