SpeechSynthesis.speak (in Web Speech API) always stops after a few seconds in Google Chrome
You asked where to report this problem. For programmers, I think this forum is the best place. In fact considerable discussion has occurred at Chrome Speech Synthesis with longer texts. But I believe much of it mistakenly focuses on the number of words allowed by SpeechSynthesis rather than on duration has you do here. In fact, your solution seems to me the most practical of all.
Google has a bug reporting facility, and the issue has been reported as speechSynthesis fails for long text without warning and blocks the API. It currently has a total of 3 reports, which give it 3 "stars." We may be able to bring attention to the issue by adding reports to this Chromium Bug (I have added one).
Current status of this Bug is "Untriaged;" also of interest are several other reported issues related to Chrome SpeechSynthesis.