2004 e46(yet another leaky)n42 318 is showing CEL and codes P0420 & p0102

Hi all, am new to this forum and would be really grateful of some help. Please let me know if I've put this in the wrong area or not provided the proper info or if this has been answered before, I did try my best to search for answers on the forum. also, thanks in advance for any help people can give me.

I'm currently driving through Europe and my e46 n42 318 touring check engine light has come on. Checked codes with my cheap and generic code reader purchased off amazon. P0420(catalyst system efficiency below threshold bank 1) and p0102(mass or volume air flow A circuit low).

Light came on while on motorway doing 80mph. Car is still running smooth at city and motorway speeds, revs are smooth at idle. Might be running a little rougher but that could just be my imagination because of the engine light. After light came on I got stuck in traffic for 20mins. When it cleared and was accelerating up to motorway speeds there was a lot of white smoke from the exhaust, this cleared after 30-60 seconds. No noticeable funny smells in the cabin. I had a look and can't see any obvious air leaks/loose hoses etc.

Car has 120k miles and was converted to LPG about 1 year ago, the conversion doesn't seem to have caused any problems since getting it done( just helped to offset the ridiculous motor tax costs here in Ireland).

Like nearly every other n42 my car leaks and drinks oil like there's no tomorrow.

So far I've replaced:
- vacuum pump gasket
- vanos solenoid o-ring
- seal on oil filler cap
- valve cover gasket
- oil separator and hoses

About 1 week before leaving I got the oil separator and hoses and valve cover gasket replaced at a BMW independent garage(wanted to try and do the work myself but left it too close to my departure date) that I've only heard good things about so I assume everything was done correctly.

So FINALLY on to my questions:
Has anybody else had any similar or have any ideas as to my next course of action and what could be throwing the codes and causing all the white smoke? as far as I could tell the separator was extremely blocked and the hose running across the manifold had completely collapsed. I'd like to avoid leaving the car in while away as it will most likely cost a fortune and I've no way of knowing how good the garage is.

Sorry for the very long winded post, I wanted to try and include all relevant info. Let me know if any other info is needed. Thanks again for any help anyone can give me I really appreciate it, cheers.