When you see __hidden_ in the crash log for function names, it means that you turned on the bitcode while exporting ipa from the archive. To be able to symbolize the failure log, you must use the module map files from the archive: 
Here are the commands you need to run in the terminal:
dsymutil --symbol-map PATH_TO_BCSYMBOLMAPS_DIR PATH_TO_DSYM
for all character map files. After this command, you can use the atos command as you tried:
dwarfdump --arch YOUR_ARCH myApp.dSYM --lookup YOUR_LOOKUP_ADDRESS
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