I have 20 files. All native 2019. We are enterprise and the design teams are on on 2018.
I have tried to export the IDML from 2021, 2020 and 2019
all give the same error.
Crashed Thread: 1 Dispatch queue: com.apple.CFNetwork.Connection
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: EXC_I386_GPFLT
Exception Note: EXC_CORPSE_NOTIFY
Termination Signal: Segmentation fault: 11
Termination Reason: Namespace SIGNAL, Code 0xb
Terminating Process: exc handler 
Thoughts? I can open in 2019 and export as well but the IDML files crash
Does the crash occur while exporting to IDML?
Or does InDesign crash when it tries to open the exported IDML file?
Could you post a sample document here in the forum so that we could test this?
What's your operating system's version?
( ACP )
I can email you a file, they are excerpts that are tagged and styled from unreleased books.
When I delete all the paragraph text frames actually the IDML opens. Hmmm
Going to load the fonts and then try to export there is only one missing link and removing that doesnt affect if the Idml opens
Running Mohave 10.14.6
Model Name: MacBook Pro
Model Identifier: MacBookPro15,3
Processor Name: Intel Core i9
Processor Speed: 2.3 GHz
Number of Processors: 1
Total Number of Cores: 8
L2 Cache (per Core): 256 KB
L3 Cache: 16 MB
Hyper-Threading Technology: Enabled
Memory: 32 GB
Boot ROM Version: 1037.147.4.0.0 (iBridge: 17.16.16610.0.0,0)
Serial Number (system): C02ZK148LVDR
Hardware UUID: EA1CAD76-84C2-5D53-AECD-C210BCD50B53
maybe an issue with the used fonts then? Can you test this on a different machine?
How are the fonts installed, are you and the team use a font management application?
Other test you can do:
Disable all used fonts. Will the IDML file open?
( ACP )
Markzware IDML converter gives me the tag mis match error,
there is my first Clue!
Hm. Could you explain in detail how Markzware IDML converter is involved in your workflow?
( ACP )
I just used that when the save as and export to IDML failed to open the said exported IDML.
I was trouble shooting