DAX MIN on Measure results in 0 without 0 in table

Question

The detailed data with booth space per customer comes from the table [ExhibitorClass_Details]. The measure [Class_Booth_Space_ALL] classifies the customer by booth space to A,B,C or D.
To be able to use this measure in visuals I have a [Class] table as well with the static values A,B,C and D.

I need to find the MAX, MIN, AVG... booth space per Class.

To calculate the MAX booth space per classicication I have created this measure:

Visual Count Class MAX Booth Space ALL = 
  VAR _rank_class = SELECTEDVALUE('Class'[Class]) 
  return MAXX('ExhibitorClass_Details', if([Class_Booth_Space_ALL] = _rank_class,
               calculate(MAX(ExhibitorClass_Details[Booth_Space_ALLPREV])),0))

My measure gives the right results for MAX.

But the wrong result for MIN:

Visual Count Class MIN Booth Space ALL = 
  VAR _rank_class = SELECTEDVALUE('Class'[Class]) 
  return MINX('ExhibitorClass_Details', if([Class_Booth_Space_ALL] = _rank_class,
               calculate(MAX(ExhibitorClass_Details[Booth_Space_ALLPREV])),0))

Instead of giving me the MIN for every class (as shown in red) it just results in 0.

Visual Count Class MIN Booth Space ALL = 
  VAR _rank_class = SELECTEDVALUE('Class'[Class]) 
  return MINX('ExhibitorClass_Details', if([Class_Booth_Space_ALL] = _rank_class,
               calculate(MIN(ExhibitorClass_Details[Booth_Space_ALLPREV])),0))

I have also tried a second version but it gives the same 0 results. Can anyone please help me.

Here is the example [ExhibitorClass_Details] data:

|Costomer_Name|Booth_Space_ALLPREV|
|Megatech|30|
|CyberMunch|210|
|Digiwell|410|
|Innovix|110|
|Cloudmore|1410|
|Systemiq|610|
|Smartsoft|150|
|Clickwell|2410|
|Weblund|170|
|Quanterra|90|
|Avantex|270|
|Ventura|150|
|Sphere|450|
|Bitling|70|
|Elementaliq|130|

and the measure for the classification:

Class_Booth_Space_ALL = 
SWITCH(TRUE(),
    SUMX(ExhibitorClass_Details, ExhibitorClass_Details[Booth_Space_ALLPREV]) >= [Booth Space ALL A CutOff],"A",
    SUMX(ExhibitorClass_Details, ExhibitorClass_Details[Booth_Space_ALLPREV]) >= [Booth Space ALL B CutOff]
    && SUMX(ExhibitorClass_Details, ExhibitorClass_Details[Booth_Space_ALLPREV]) < [Booth Space ALL A CutOff],"B",
    SUMX(ExhibitorClass_Details, ExhibitorClass_Details[Booth_Space_ALLPREV]) >= [Booth Space ALL C CutOff]
    && SUMX(ExhibitorClass_Details, ExhibitorClass_Details[Booth_Space_ALLPREV]) < [Booth Space ALL B CutOff],"C",
    SUMX(ExhibitorClass_Details, ExhibitorClass_Details[Booth_Space_ALLPREV]) >= [Booth Space ALL D CutOff]
    && SUMX(ExhibitorClass_Details, ExhibitorClass_Details[Booth_Space_ALLPREV]) < [Booth Space ALL C CutOff],"D",
    "N/A")