I recently had my IP overhauled. I don't use biodiesel but did use a couple of tanks of WVO blend (10% ULP) amongst about 20 tanks of dino. The pump man asked "Have you been using bio" as he found evidence of residual veg oil in the output valves and reckoned the valves were 'sluggish'.
He told me not to use beyond 5% bio (B5). He showed me some documentation from the association of diesel fuel equipment manufacturers regarding fuel types and warranty.
It showed pictures of Zinc plated and Cadmium plated components from IPs where the plating had been removed and some of it had apparently flaked off and caused damage and blockage.
The documentation stated that for any warranty claim a fuel analysis was required and if more than 5% bio (they call it FAME - fatty acid methyl esters) is found then claim is rejected.
So my pump man said - sure, go ahead and use bio - but remember there will be no warranty.
I had heard that bio was not compatible with zinc but not heard about cadmium before.
Would a high quality well washed bio have the same effect? This guy was talking commercial bio and also went on to talk about poor quality dino and said you need to be careful where you buy your fuel.

Also the documentation mentioned "Unmodified Vegetable Oil" as fuel and said nothing about it causing actual damage - just gumming of the IP - sticky output valves etc.
I have concluded that it must be acid in the bio that can do damage and it would be during overnight stops with the IP full of bio that would give the acid time exposure to do its job.
Similarly with the VO gumming, it would (I imagine) be the VO overnight in the cooling IP, thickening and forming gum.

So - for me it will be 2 tank with VO for driving and a thorough purge to dino for overnight stops and the occasional flush with B100 (if I can get it) or ATF, to remove any residual gum.

I wonder if it might be wise to go to a 2 tank system if using bio so that the IP can be left full of dino overnight.

Zinc and cadmium are both easily oxidised metals. In the presence of even small amounts of FFAs it's reasonable to expect they'd degrade.

In terms of the reactivity of zinc with B100, it's possible. Zinc is probably the most easily oxidised metal that there is. The ester group in a methyl ester molecule is generally not considered to be an oxidising group, but it's possible that it could act as an oxidiser in the presence of such a strong reducing agent as zinc (reducing agent = easily oxidised material).

Gumming is caused by UV oxidation of an unsaturated lipid chain. The more unsaturated it is, the more likely it is to occur. Unfortunately, it also true that the more unsaturated the lipid is, the more likely it is to be a liquid, and it's much easier to handle liquid oils when making bio then solid fat.

The relevant measure is its iodine (or bromine) number. The higher it is, the more unsaturated it is, and the more prone to "gumming"

I think sodium, lithium and caesium might suggest otherwise (well, all of the alkali metals actually), but that aside, I have come accross similar problems before - with mineral oil.

I had to investigate some glugging problems in galvanised oil to air heat exchangers a few years ago.

If I remember correctly, the problem was that there was water in the oil, and the combination of oil, water and zinc was causing saponification.

I don't know if a similar reaction is the cause of your problem (as Mark mentioned, FFA's could also be a culprit) but it could point to water in the system.

I can't see UV being much of a problem, unless you store it in uv transparent containers (not much UV radiation in a fuel tank), however it's not the only way to saturate a double bond.

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