ast_yyerror (syntax) breaking outbound trunks

I'm not sure if this is related to 21000 but I'm asked to create this ticket. Trunks are breaking on outbound calls (inbound working fine) with the error you see in the logfile I provide, specifically. . .

[2020-02-17 22:25:53] WARNING[16368][C-0000002b]: ast_expr2.fl:470 ast_yyerror: ast_yyerror():  syntax error: syntax error, unexpected '>', expecting '-' or '!' or '(' or '<token>'; Input:
"LIMIT"="LIMIT" & 4 & 0 & >0 & 0>=
                         ^
[2020-02-17 22:25:53] WARNING[16368][C-0000002b]: ast_expr2.fl:474 ast_yyerror: If you have questions, please refer to https://wiki.asterisk.org/wiki/display/AST/Channel+Variables                                                                                                                                                                                                                                                                                                                      
[2020-02-17 22:25:53] ERROR[1465]: res_pjsip.c:3533 ast_sip_create_dialog_uac: Endpoint 'Twilio_UK_0800': Could not create dialog to invalid URI 'Twilio_UK_0800'.  Is endpoint registered and reachable?
[2020-02-17 22:25:53] ERROR[1465]: chan_pjsip.c:2649 request: Failed to create outgoing session to endpoint 'Twilio_UK_0800'                                                                                                                                                                                                                                                                                                                                                                             
[2020-02-17 22:25:53] WARNING[16368][C-0000002b]: app_dial.c:2578 dial_exec_full: Unable to create channel of type 'PJSIP' (cause 3 - No route to destination)

This started happening when upgrading to 15.0.16.42

Trunk settings are as follows. . .

[Twilio_UK_0800]
type=endpoint
transport=0.0.0.0-tls
context=from-pstn
disallow=all
allow=ulaw
aors=Twilio_UK_0800
send_connected_line=false
language=en_GB
outbound_auth=Twilio_UK_0800
t38_udptl=no
t38_udptl_ec=none
fax_detect=no
trust_id_inbound=no
t38_udptl_nat=no
direct_media=no
rewrite_contact=yes
media_encryption=sdes
rtp_symmetric=yes
dtmf_mode=rfc4733

Thank you for your kind attention