0.5mm thin wall regular gaps (2 replies)

Hi,

I've recently changed my hotend but my nozzle diameter is still 0.35mm. Problem now is that at regular intervals on the 0.5 mm thin wall it looks like the hotend is not extrduing enough PLA.
I've recalibrated the e-steps but don't know what's causing this.
Only started when I replaced my hotend to a j-head.
Previously the thin wall was printing fine.

Any ideas what might be causing this?