Filebeat can't load template due to circuitbreaker

I'm upgrading elasticsearch/filebeat from 6.5.2 to 7.3.0

filebeat is failing to start with this error:

Error loading Elasticsearch template: could not load template. Elasticsearch returned: couldn't load template: couldn't load json. Error: 429 Too Many Requests: {"error":{"root_cause":[{"type":"circuit_breaking_exception","reason":"[parent] Data too large, data for [<http_request>] would be [1005387694/958.8mb], which is larger than the limit of [1003493785/957mb], real usage: [1005306456/958.7mb], new bytes reserved: [81238/79.3kb], usages [request=0/0b, fielddata=0/0b, in_flight_requests=81238/79.3kb, accounting=88508810/84.4mb]","bytes_wanted":1005387694,"bytes_limit":1003493785,"durability":"PERMANENT"}]

Full error message which shows a massive template being uploaded:

I tried increasing swap on the ES box, and increasing java -Xmx/-Xms

Is this somehow due to using setup.template.append_fields? It was working fine in 6.5.2

Had to upgrade filebeat to 6.7.2 before upgrading to 7.3.0