I have the same issue with my text to speech when setting up respond to events. The best work around I have found is described below as best I am able, it requires some testing on your part.
Send text to device, 21 (my main tv orbiter)
"Motion has been detected"
Send text to device, 21
"Motion detected on the driveway camera"
I do two separate announcements, the first message for motion is always the same and not specific to location. I find this is enough to get my attention and allows me to pay attention to the second message. About half way through the first announcement I am now listening closely to what cam went off.
Test command and listen to what words are not clear or are getting cut off. Below in red I am showing what word is cut off
*Motion has been
detected*Motion detected on the drive
way cameraNow I move the words in red onto their own line, this is tricky though because it doesn't seem to drop off words based on message length. So it would leave off any word I leave last. Here is how I did it:
Send text to device, 21
"Motion has been, d"
Send text to device, 21
"Detected, m"
Send text to device, 21
"Motion detected on the drive, w"
Send text to device, 21
"way camera, end"
Experiment with that, it was frustrating for me as well because the rules of it leaving off a word could not be easily predicted. When using 8.10 I also had some success using spaces and commas to separate phrases as the words seemed to move too quickly. An example would be ",Moe schion has, Ben , detec Ted ,d"