What does internet explorer report as capacity/free space of share when you try to copy largeish file and fail? If the free space shown corresponds to the message about missing space, then it would seem like SMB service, running in ROS, somehow rolls over at 1GB (which is 2 to the power of 30) and reports low number to client ... which should be fixed of course.
Thanks mkx. Your response was very helpful. Assuming that by "internet explorer" you mean "Windows Explorer" which is the file manager and not the web browser, it is reporting 531MB free space of 1.4GB total size which is strange because the drive is a 500GB USB. I had to map the MikroTik shared drive in Windows before it showed up in Windows 10 as follows:
The USB drive is different than the earlier one as I wanted to make sure that the problem wasn't related to a defective drive. It is a 500GB Western Digital PCIe SSD mounted inside a Thunderbolt 3 / USB 3.1 Gen 2 case:
WD_BLACK 500GB SN750 NVMe Internal Gaming SSD Solid State Drive - Gen3 PCIe, M.2 2280, 3D NAND, Up to 3,430 MB/s - WDS500G3X0C
https://www.amazon.com/gp/product/B07MH2P5ZD
Plugable USB C to M.2 NVMe Tool-free Enclosure USB C and Thunderbolt 3 Compatible up to USB 3.1 Gen 2 Speeds (10Gbps).
https://www.amazon.com/gp/product/B07N48N5GR
So I'm not suspecting any problems with the drive since I'm experiencing the exact same problems with it as with the one I described in my earlier post. When I copied the 882MB file to it, the transfer speed that Windows reported was 80MB/sec which is very fast and shows that MikroTik's RB5009 USB 3.0 port is an improvement over their USB 2.0 ports. I formatted the drive using Linux gparted and selected msdos for partition table type and ext3 for file system type.