Ask HN: Signal on Android not receiving iPhone texts?

I am sharing this partly to resolve it, partly to warn others to not rely on Signal until this is fixed. I set Signal up on my Pixel 2 (Android 8.1 but updated to 9 last week) as my default texting app. Over the past month I've missed SMS texts from at least two work colleagues' iPhones (and goodness know how many others). They do receive my texts though.

Has anyone else experienced this bug? Am I doing something wrong in setting Signal up as my default texting app? How can I fix this? Are there other apps I ought to use instead? I haven't researched the stock Google messaging app but try to stay away from them as much as I can for privacy; is it pretty secure? In the interim I'm switching back to the stock Android texting app as default, and recommend others do the same. Delivered > encrypted.

I have messaged Signal via https://support.signal.org/hc/en-us/requests/new and am waiting for a reply. A cursory search online shows no problems like this so far though.