Telegraf getting 400 errors

Backgroud:

I set up a TLS reverse Proxy which works fine for a lot of other services but for influx I keep getting the following:

2018-10-27T15:06:00Z E! [outputs.influxdb] when writing to [https://influx.some.where:8086]: 400 Bad Request
2018-10-27T15:06:00Z E! Error writing to output [influxdb]: could not write any address

Configuration posted here: TLS configuration with telefgraf and influxdb behind nginx proxy TLS Termination endpoint - #2 by drahnr