It appears that IOS 12 has removed functionality of being able to pause music while providing voice navigation (turn by turn) using Apple Maps. Spoken audio can be paused but not music according to this article (https://support.apple.com/en-us/HT204242) Any reason why this has been removed? While i am listening to music all i get now are dings which if your not looking at the phone is not helpful at all.
I did some more testing and it appears this behavior only occurs when using Amazon music. If i use Pandora the "turn by turn" prompts are still heard while music is playing. I found this related post
https://discussions.apple.com/thread/8555688
Pausing music has never been an option. Only pausing spoken audio.
Congratulations you just linked the exact same article from my original post which states that the pause audio option does not work for music. Even if you use the iphone has the audio source play some music then open maps and use navigation the "turn by turn" prompts are not heard instead they are replaced with beeps
Agreed, but previously music got quieter during navigational "turn by turn" prompts. Now while playing music only beeps are heard. I have tested this on an Iphone 5 i have which is on IOS 10.3.3 so i know for a fact that "turn by turn" were previously given while playing music on older versions of IOS
I discovered that this issue is caused by enabling the hands-free alexa option. If you disable the option and restart the app you will again have voice navigation prompts while listening to music.
Use Maps and Bluetooth on your iPhone and iPad
Learn how to use Maps on your iPhone or iPad with a Bluetooth accessory.
Manage your Navigation Voice settings
First, pair your iPhone or iPad to your car or Bluetooth accessory. Then follow these steps to manage your Navigation Voice settings when you’re getting turn-by-turn directions:
, Maps will start turn-by-turn navigation. Tap 
to open the Route Card.You can also control settings to pause the audio during navigation or control the audio output from your iPhone or iPad. When audio plays, the audio output can only be managed from Control Center on your iPhone or iPad.
Allow Navigation Voice Prompts
Hands-free profile (HFP) allows navigation prompts to play through your car speakers when iPhone isn't selected as the audio source. If you don't see the HFP option, your car stereo might not support it. Check the user guide for your car to see if your stereo supports HFP.
If you don't see the HFP setting when your iPhone is connected to your stereo, check with the stereo manufacturer. The HFP feature depends on your car stereo.
Use Maps and Bluetooth on your iPhone and iPad - Apple Support
https://support.apple.com/en-us/HT204242
IOS 12 Maps Navigation Voice Navigation
