When trying to import staged marc records, it freezes at 4 %; another file freezes at 0%. Both files are over 6,000 records in length. The same happens on KOHA 21.11. On the contrary it accepts an import file of 1,700 records. Thanks for your assistance.
Have you tried waiting it out? The progress bar not always working nicley is a known thing, but in the background the import might still work and finish correctly. You could try a report on import_biblios to see if there is still 'movement' while it gets stuck and more lines are added there. There is also ongoing work to improve the imports with 27421.
Bug 30738 will also help with this, since right now fatal errors that cause an import to crash aren't logged anywhere.
I think this is probably a duplicate of bug 30739 *** This bug has been marked as a duplicate of bug 30739 ***