That is surely not normal.
I am running the latest 3.90 Z620 BIOS and in the HP drivers section for the Z620 they really seem confused. That BIOS shows up as being for the Z420, Z620, Z820, and does not show up as the latest BIOS for a number of Z620 operating systems.
It is, in fact, for the Z420 and the Z620. 3.90 is the latest, not 3.88.
I'd clear your CMOS as is properly done following the instructions in the technical and service manual exactly. Make sure that all peripherals are unplugged (they can feed back power into the motherboard even if it is off), and the main power cord must be unplugged for enough time that the capacitors unload.
I run all our Z620s in legacy mode, and if you PM me with your email address I can send you my hand tuned Z620 replicated setup file that lets you clone my settings. Read up on Replicated Setup in this forum, if you wish. This is for Z620s running off a single SSD, with a documents HDD. The tuning is a bit different for whether you run 1 or 2 video cards.
I usually update BIOS from within BIOS, but for this update I did it using the HPQFlash from the SoftPaq and all went well. It is a big update, and took over 5 minutes.