Help solve the mystery of my hefe’s fading flavours

My last 2 hefe’s have tasted so fantastic 1 to 2 weeks after bottling (excuse the boasting but that's how proud I felt after those tastings)!

However, by week 3 the flavor intensity from both batches is already lighter and by week 4 onwards the flavours are so obviously faded that they taste like they’re diluted with water ie thin-bodied, dry-ish, no more malty sweetness and the banana aroma is vanished. Now, I’m aware hefe’s are not meant to be kept for “long” but surely 3 weeks from priming is unusually short.

This is a follow-up to my earlier post on the 1st problematic hefe batch and I can rule out the suggestions from there on this second batch which were “oxygen exposure” and “conditioning too warm” (https://www.homebrewtalk.com/showthread.php?t=569486).

Additional data points for both these 2 batches are: 1) my first times using WLP300, 2) my first times to do ferulic acid rests and 3) none of my other beers have this accelerated fading of flavours including my saisons, wits and kolsches.

Here’s the recipe:

38% Pilsner
38% Pale wheat
19% wholegrain wheat flour
5% Caramunich III
2oz hallertau
1 vial WLP300 (1.5L starter)

Mash:
Cereal mash
Ferulic A-rest 45C/113F 20mins
P-rest 50C/122F 8mins
S-rest 69C/156F 40mins
Decoc 1/2 grains 10mins
Mashout 69C/156F 15mins
Dunk sparge 77C/171F 10mins
PH (10mins into S-rest): 5.4 for batch 1, 5.5 for batch 2

Fermentation:
17C/63F 2 days -> 20C/68F by day 5 -> 18C/64F for 2 weeks

Conditioning:
Sugar primed, 72F week 1, 50F thereafter

Thanks, gurus.

Have you tried swirling up the yeast into the beer and pouring that into the glass? My assumption is the yeast is dropping out of suspension dragging the yeast character with it.

Definitely did! I routinely stir up the yeast of my hefes before pouring. Good suggestion though.

Can I definitely rule out the ferulic acid rest causing progressively thinner beers?