Small update: since I installed the used Bosch MAF with the adaptor cable, I haven't gotten the DTC, I took it to mild mountains and so far so good, now I gotta take it to the beach and check there.

@T5-T6-Schnappi I thought the same, however several other cars ive seen here are using the same MAF with adaptor cable and even is sold as a kit with the adaptor cable. I found an original Bosch MAF with the same half/square connector and installed it, havent gone to the mountains to test it yet though, will keep you posted.

@T5-T6-Schnappi My barometric pressure does fluctuate correctly according to the elevation, which is the weirdest part. I am planning on testing my MAF with a borrowed proven one as they are very rare here in my country, however my mate that can lend me the MAF is out of the country for a couple of weeks.
Wiring seems OK, connections to the MAF seem ok, however my engine uses a "round" connector 4 pin maf, and it has been replaced with a "semi square" connector 4 pin maf with a conversion cable.
I checked all vacuum connections and all are working as intented, also I believe vacuum leaks wont affect a diesel as it uses a mechanically driven vacuum pump, or am I wrong?
Im running original, stock air filter.

Many thanks for your help!

I am having the same issue, however I have noticed that not all parameters freeze the program when selected.
In my case VDash freezes whenever I select specific parameters and then click "start".

Ok so I loaded a Stage 2 + egr+dpf off remap and MOST problems were solved except the barometric issues, so its safe to say there is something wrong with the baro sensor indeed.
I took the car high up into the mountains and in random intervals when I was not touching the throttle the "MAF sensor reading too high" DTC popped up.

Is there anything I should check before replacing the ECU?

@T5-T6-Schnappi Thanks for your reply!
EGR has been blanked and MAP has been cleaned.
I am completely unsure these errors appeared with the original factory map, hence I would like to try remapping first.

I will proceed to remap the following days and post updates.

I am diagnosing the ECU in an XC90 D5 2009 as the barometric sensor seems to be causing trouble, car drives perfect in the capital (San José, Costa Rica), however, as soon as the car is driven to higher or lower elevations, it starts throwing MAF and EGR codes: MAF signal too high, MAF signal too low, EGR flow too high and EGR flow too low. These codes are thrown randomly when engine braking, and alternate between "EGR flow too high/MAF signal too low" when driving in high atmospheric pressure areas (i.e. when going to the beach), or "EGR flow too low/MAF signal too high" when driving in low atmospheric pressure areas (i.e. going to a mountain). The ECU has been several times remapped by a local tech in order to increase power and attempt to solve the problem, the DPF and EGR have also been supposedly deactivated.

My question is: If I connect the car to VDash and purchase a Stage 2 remap, is the remap based on the original map that is downloaded from the ECU? Or is it based on a general map the lads over at D5T5 use?

I would like to try remapping the ECU with VDash before replacing it in order to discard potential issues with the remap, however I am worried about the local tech's map interfering with the remap.