Thank you for reporting. I've reproduced the problem and I'm looking in the issue.
The implementation of the algorithm seems correct in PeaZip, and as for I was able to see the underlying library provides consistent output for all utilities it is implemented in.
The problem is that multiple CRC64 standards exists, see in example http://reveng.sourceforge.net/crc-catalogue/17plus.htm#crc.cat.crc-64 and https://en.wikipedia.org/wiki/Cyclic_redundancy_check#Standards_and_common_use
My software uses Wolfgang Ehrhardt's implementation (which is also used in a plugin for FAR Manager maintained by Wolfgang Ehrhardt himself), identified as CRC-64/WE in first link, while 7-Zip / p7zip uses Igor Pavlov's implementation (he is the author of 7-Zip, and of 7Z and XZ formats), identified as CRC-64/XZ in the first link.
While the algorithms are commonly referred with same name, they are inherently different and produces different results. I'll test better the issue, and I'll try to clarify the topic in documentation in future.
PeaZip
? Gtk2 and 7z Windows, check sums not the same on the same files. But 7z the same file say the identical sum in Windows (~2 month ago I check CRC64 with other file and check now CRС64). File on Ext2, VBox lan disk (lan folder). files are not moved from disk partition for checking.
https://s3.postimg.org/g5mmpbmo3/q5ete654grhd7eyefh.png