Thank you for these replies!
Foremost allow me to clarify that the detail provided above serves to provide context and avoid you having to ask questions to some of the more obvious or common things relating to an issue of this nature. I appreciate that to the trained eye some of these aspects may not be relevant. Sadly my eye is untrained and there are many possible causal links...
Regarding the contentious hull anode, I'm the second owner of this boat. I confirmed with the first owner, who is based in Thailand, that Bavaria indeed did fit the hull anode ex-factory as an option for deliveries in tropical climates. They confirm that the other Bavaria's in their fleet, even before this time, also had this fitted ex-factory. This seems to check out since the cable connected to the hull anode is inside a sleeve with other factory fitted cables, including the fuel sender, and some engine wiring. Like tiger79, mine is also fitted slightly forward and off to starboard side of the saildrive. On the inside its under the aft-berth close to the diesel tank. So seems this was something that was maybe not common for the European and/or American market, but certainly for the tropics. Given that my hull anode has shown no wear in the last two years, I agree with symphony2 that it's not doing anything.
I should also add that I've changed all my thru hulls to Trudesign two years ago, so the only metal under the water is the keel, saildrive, prop and the bit of the rudder shaft that comes into contact with water as the boat rides the swell.
For context, I've been in touch with Flexofold for the past 18 months regarding this issue and their response has been fairly unhelpful. They attributed this rapid wear to the current/flow on the swing mooring and warm water temperature, and have happily sold me 13 sets of anodes which I've replaced at great effort every other month. I've more recently been in touch with them again and have had swift replies from them, although not entirely helpful either in resolving the matter. I'd like to think there isn't anything sinister about the fact that they are aware of this and have subsequently released a new composite model, since there are equally many happy owners taht are not facing the same issues as I am, and will instead try to understand what is different or unique in my application which could be causing this issue.
I agree with you that the rate of anode depletion on the prop is unusually high, hence the reason I reached out here for opinion and advice.
Regarding the stray current, this has been foremost on my mind, but I did have a marine electrician test for stray current with the boat in the water, and then do some further testing when she was on the hard in December, and he reported no issues. All values were around -1,000mV which he said is normal and correct in salt water. But I think I need get a second opinion on this and have today ordered a Corrosion Reference Electrode from BoatZincs.com to test for myself. I will report back once I receive it and have done the tests.
So the issue of the prop isolation seems to be something to look into. As Yngmar points out, the prop should be isolated from the saildrive, which is achieved by a bushing inside the prop hub. Flexofold today confirmed that there are two plastic inserts that separate the bronze bushing on the drive shaft spline from the bronze prop hub. It seems that this bushing is a potential failure point, since the spline insert can push into the hub causing it to make contact, which may be exacerbating my issue as implied above. On this model of the Flexofold there isn't a plastic washer on the end-nut as described by Yngmar so I can confirm that there isn't any omission there. I've removed and refitted this prop three times (myself) already, and followed the instructions in the manual to the T every time. But as I recall, there WAS conductivity between the prop and the saildrive, and I suspect herein lies the crux of some of the issue. Unfortunately the manual doesn't specify an electrical test to check isolation (like the VP manual does) nor states that the prop must be isolated electrically from the drive shaft. Maybe it's common knowledge for some but it certainly wasn't for me!
I also learned today that it is not uncommon for anodes on a hub to show greater/accelerated wear due to the increased friction caused by the flow across the anode as the prop spins. Apparently this is also an issue facing Gori props with protruding anodes on the hub. I'm ruling this out for the time being since I haven't used the boat in 6 weeks as I was abroad, and the rate of wear has remained alarmingly high.
Then there is the issue of the dissimilar anode material, which Flexofold has implied could have an impact, but as they do not sell aluminium anodes for this prop, suggested I change the saildrive anodes to zinc instead of changing the prop anodes to aluminium, and continue to monitor the situation. I was able to order aluminium anodes for this prop from BoatZincs.com which will come together with the Corrosion Reference Electrode. I'm going to fit both the zinc and the aluminium anodes on the prop alternately to test the corrosion potential of each respectively.
Thank you again for your thoughts and replies above!