Crazy problem with google_translate_say

I have a couple of HA automations that respond to a Google voice command and read out the values of various household sensors. Lately the response has been very erratic, and a couple of days ago it quit working entirely. The problem is that google_translate_say is reporting a generic unspecific error. The first few time it worked again after restarting HA, but now that doesn’t help. However several other routines I have in Node Red that use google_translate_say continue to work just fine. So I figured I would try recreating the failing automaton in Node Red.
Only to encounter a very strange problem! If I create a new node using google_translate_say in Node Red, it fails with an api error. But if I copy one of my existing nodes that uses google_translate_say, it works fine. Until I modify the text of the message even slightly - then it fails too.The settings of the new and old nodes are identical, but the new one fails and a copy of the old one doesn’t!
I thought it might be some kind of new fault with Node Red linking to Home Assistant that only affects a new node, since I haven’t had occasion to restart Node Red for a few weeks. But I have restarted Home Assistant many times, so that doesn’t feel like the right explanation.
Any ideas?