Sorry, I thought you were talking about using Orbot with Amber for signing, not using Orbot with Coracle for loading content from relays or writing events to them. The order in which you listed them ("Orbot+Amber+Coracle Android") seemed to imply that.
Not sure why you are having issues with signing with this setup. I have Coracle set up to use Orbot and am still able to sign via Amber without a problem. As mentioned above, Amber signing happens locally, so connecting Coracle via Tor shouldn't affect it at all.