The extra-framework Al may block the micropores or connectivity between micro and mesoporosity which you created by adding KOH (desilication). I think you have to wash your zeolite with HCl after desilication to remove this extra-framework Al, and try to ran N2 sorption once again.

Or if you don't want to do the HCl washing, try ran N2 sorption but with more zeolite sample.

good luck!

It sounds like you have destroyed the zeolite structure and any porosity has collapsed so the BET measurements are low.

Which equipment you are using? How much is the sample amount (maybe too little)? Which temperature did you use for degas? How long did experiment take (maybe too long)?

Even is the structure is destroyed, desorption branch cannot go up (step at 0.7 Pr), so maybe something wrong with the measurement.

I think that this is just experimental mistake. Try again very carefully. Check the vakuum system and the burette!

Good luck

may be degassing problem or sample amount, u should use small cell for measurement. do the degassing properly run again.

 which instrument u r using micromeritis  or Quantachrome

It seems to me that something was wrong with the measurements. Try to do this again and do the blank of empty burette first 

Considering blue line is for desorption, gas desorption is more than adsorbed at certain pressures.This usually occur when degassing is  not done properly. also if the transducers malfunction occur during desorption while attaining required pressure result in such isotherms. Isotherm looks like that Type IV due to step wise adsorption pattern.

I have seen this type of noisy isotherm often when trying to measure will too small a sample.  Make sure you use filler rods and the smallest sample cell you have to minimize dead volume, and maximize the amount of sample.  If the isotherm is still noisy then it's probably an issue with degassing or an "unclean" sample.  Good luck.