Just my 2 cents, Lebara unlimited is great but I noticed that once I put the sim card in my D-Link DWR-921-E383 4g/LTE router,the day after, the kids' Amazon tablets started to have issues while trying to stream YouTube/Kids and me too..I don't think it was the APN settings the problem,it didn't matter if I used the wap.vodafone.co.uk
or the uk.lebara.mobi; I think they apply some filtering if you stick the sim in an unrecognized device different from a phone.
My solution was to to use Cloudflare's DNS in the router, I used the family ones: 126.96.36.199 as primary and 188.8.131.52 as secondary.
After that everything was back to smooth normal.
Hope it might help someone with similar situation.