Unable to dial LOCAL/XX from TAPI since FreePBX 15

I'm using Phonesuite for Asterisk as TAPI driver to make calls from Windows.
The user has multiple phones connected using PJSIP (max contacts > 1).

Problem: When dialing PJSIP/18 only one of the phones is ringing (presumably the one which has most recently registered). This seems to be normal PJSIP behaviour.

The solution that was suggested was dialing LOCAL/18 instead, which then rings all PJSIP contacts. This was working fine in FreePBX 14, but updating from FreePBX 14 to FreePBX 15 has reproducibly destroyed this functionality (tried on multiple machines). Now with FreePBX 15, when dialing LOCAL/18 (context: from-internal), the following error appears on the Asterisk console:

[2020-06-18 14:00:33] NOTICE[22884]: core_local.c:734 local_call: No such extension/context 18@default while calling Local channel

Could the functionality to dial LOCAL/XX extensions please be fixed? Or another way to invoke PJSIP_DIAL_CONTACTS so all phones ring from TAPI would be welcome of course as well.