I'm so sorry. You had enough to deal with already. .
I did quick search in this forum and didn't see any posts about it.
I then a brief Google scholar search and found a couple interesting reports. It sounds like NTM has been recognized as a cause for elevated levels for several years and may be caused by inflammation.
https://www.researchgate.net/publication/322149549_Bronchiectasis_as_a_Cause_of_Elevated_CA-19-9_Demonstrated_on_18F-FDG_PETCT
Only the abstract was available free.
""64-year-old woman with a history of weight loss and a markedly elevated serum carbohydrate antigen 19-9 level of 560 U/mL was referred for an F-FDG PET study to evaluate for occult malignancy. In addition to the weight loss, she had suffered from a chronic cough secondary to bronchiectasis and had been investigated for a suspected gastrointestinal malignancy. Multiple FDG-avid foci were detected throughout both lungs on FDG PET, corresponding to areas of bronchiectasis on CT with no obvious suspicious FDG-avid foci elsewhere. This supported an inflammatory process causing her elevated carbohydrate antigen 19-9 rather than malignancy."

Here's another pretty detailed one.
https://www.bjid.org.br/en-elevated-serum-ca-19-9-levels-articulo-S1413867015001944
Good luck to you and keep us posted.