Since the update to DOpus 13.3 (and the problem persists in 13.4), when I copy files through local network, Windows 10 during copying is having performance issues and freezing. Copy progress works, but copy speed is lower than it should be (1Mbps Network, copy speed before 13.3 was around 110MB/s, now is around 43MB/s). And, Task Manager shows 'System Interrupts' and 'System' processes to have high CPU usage (10 to 20% each), and first CPU core is at 100% overload, while all other cores are around zero and Ethernet connection tops at 300Mbps.
Once the copy process is finished, all goes back to normal, CPU cores work normal, System Interrupts and System processes go back to normal (at 0%), and computer can be used again. And, if I pause copy process, everything goes back to normal, as soon as I resume it, again everything returns and computer is unusable. It seams that copy process only uses first CPU core. I tested Windows Explorer copy to same network machine, there are no issues, copy process is faster (goes to 100MB/s) and it is not utilizing first CPU core like DOpus does. When I copy files from one drive to anthor drive on the same machine, it works normal, problem is only network copy.
I have DOpus 12 on one machine, and it works fine with same copy process.
Nothing changed in 13.4 regarding how files are copied, which is done by Windows in any case.
Unless you've changed Preferences / Miscellaneous / Advanced: [Filesystem] copy_allow_delegation to False, Opus just tells Windows which file to copy where and reports the progress of it. Opus itself isn't involved in the copy normally, unless that option is changed or the source/destination isn't a normal directory (e.g. archives).
If you're seeing speed differences and high CPU usage after installing 13.4, it's likely to be antivirus or firewall doing something stupid, possibly because 13.4 was signed with a different key to usual, which some antivirus freaks out about. (Each of us has our own key, so some releases will be signed by different people depending on who built them. Mine signed 13.4 and has been used less often, so it hasn't been seen by antivirus as much.)
Note that Defender is one of the worst antivirus these days.
It is not antivirus or firewall related. I tested with disabled Defender, bacuse I suspected that it may be causing problems, I do not have any firewall in local network.
I have noticed the problem in 13.3, and in 12 there is no problem during network copy. I tested with Windows Explorer, and there are no copy issues, only with Directory Opus 13.
(Apologies, I misread that the issue started in 13.4 rather than 13.3, although there wasn't a change in 13.3 either in terms of how files are copied.)
Task Manager attributing things to System Interrupts / Processes suggests the issue is on the driver/kernel/antivirus side of things, at least. That's not something user-mode software like Opus could trigger by itself, as no Opus code runs inside interrupt handlers.
There are several threads on the web about similar issues, but I don't know if they'll be relevant as the cause seems to be different on different machines.
Maybe a recent network driver update (e.g. via Windows Update)?
Changing copy_allow_delegation to False in Opus may mask the problem, since the copy will be done in a different way (which doesn't saturate the network quite as much), but I would still want to get to the bottom of the real cause, as a lot of software uses CopyFileEx to copy files around (which is what Opus uses by default, when copy_allow_delegation = True).
It was the network adapter drivers. Gigabyte update software recently updated Realtek Ethernet drivers, so I now deleted those drivers, and let Windows install default once, and things are back to normal.