I don't know what is your problem. I opened the file changes.txt in program files folder of UltraEdit having 2.215 lines in UltraEdit v24.20.0.51 with all settings set to default. I pressed Ctrl+A, Ctrl+C, Ctrl+N and several times Ctrl+V until having 50.923 lines in new ANSI encoded file with a file size of 2.680.742 bytes. I saved the file first as Test.txt and second as Test.php to enable PHP syntax highlighting on this file not containing PHP code. On pressing Ctrl+A on both files I could see that UltraEdit temporarily displayed end of file before displaying top of file with everything selected. The time for selecting the entire file content depended on syntax highlighting. Selecting everything in Test.txt with no syntax highlighting was a bit faster than selecting everything in  Test.php with syntax highlighting. But nothing changed at all on pressing next Ctrl+C. There was neither the document window refreshed nor was the mouse pointer changed on copying the selection to clipboard.

I could see a very short delay on pasting with Ctrl+V the copied 50.923 lines somewhere inside Test.php. But with syntax highlighting enabled, with code folding enabled, with line change indication feature enabled, with undo feature enabled, etc. it is explainable that UltraEdit takes some milliseconds on pasting a block with 50.923 lines into a file with having already 50.923 lines to update all the data accordingly.

You could disable the line change indication feature for this file or by default for any file to speed up editing a file. I don't need the LCI feature. Therefore LCI is disabled in my configuration while it is enabled in default configuration used for this test. Open Advanced - Settings or Configuration - Editor display - Line change indicator and uncheck setting Enable line change indicator (LCI). Then LCI is by default disabled, but can be individually enabled for a file by clicking on item Line change indicator on ribbon tab View.

You could also close the Document map view if you don't need this view as I have done in my configuration. Right click into the document map view and left click on last context menu item Close document map or toggle off this view via check box item Document map on ribbon tab View. That speeds up editing files too.

Do you not need the line numbers displayed on left side as the line number of active line in status bar at bottom is enough? Yes, then toggle off displaying line numbers on ribbon tab View by clicking on Line numbers. Extra hint: Open Advanced - Settings or Configuration - Editor - Bookmarks and enable Highlight entire line and switch in configuration to Editor display - Code folding and uncheck Enable show/hide lines and code folding and Enable show/hide lines in non syntax highlighted files to speed up editing files and additionally get more horizontal space for document window area.

Do you not need the ruler at top because the column number in status bar at bottom is enough for you? Yes, then toggle off displaying the ruler on ribbon tab View by clicking on Ruler.

Summary: Look on all ribbon tabs and all configuration settings and disable everything you don't need. Help is available for every setting and every item on a ribbon tab.

Go to previous position is listed with name Back (last position) in commands list and Go to next position with Forward (next position).