Hmm. I see no acid addition. With so much pilsner malt with very little specialty malt, and somewhat alkaline water source, your mash pH could be quite high about 5.8 or maybe even higher. This could lead to additional extraction of tannins, phenols, etc. So then your bitterness might not be so much from IBUs as from some other unwanted extracted thing. I'd aim for mash pH closer to 5.5-5.6 (as measured at room temperature).
Exactly. Alkaline water will enhance bitterness, but not in a good way. High pH at pitch can lead to higher pH in the finish. Your lager should land at 4.2-4.3 in the finish beer. Higher finish pH will lead to a higher perceived bitterness. The lab report will give you some information and may or may not be useful, but in the end the human palate rules the roost.
Often homebrewers will get the pH right in the mash and never check it at pitch, it almost always rises after sparging even with RO water. Your pitching pH should be 5.1-5.2 ideally. A mash pH of 5.4 is great for mashing, but too high for the pitch.
Edit: The way to test if the pH is too high is to pour a half a glass or so and add 88% lactic or 85% phosphoric acid one drop at a time with a tooth pick. Taste it after each drop and note the bitterness. When you taste the acid you can stop. If the bitterness drops, it's likely your pH is too high in the finished beer.