After hitting "Fetch Last Page" the results are updating in the results window. However, I cannot use the horizontal or vertical scroll bars while the query is still in progress. I was able to do this in v14. It doesn't seem to work in v15.0.4. Do I have to wait until the last page is fetched before I scroll through the (partial) results?

This works the same in 14.0 and 15.0. Can you go to Preferences > Oracle > Connection and check the "Session Mode" preference? If it is set to "Single Session", can you set it to "Dual Session" or "Multi Session", restart PL/SQL Developer, and try again?

Multi Session was the setting in v14 and it is also the setting in v15. Allow multiple connections is also checked. When a query is active, I cannot scroll nor can I click on the connected session indication at the bottom of the window in order to bring up the "Recent" selector. If I go to another sql window and try to log in I get the dialog box with "You cannot log on as another user while one or more windows are still executing".

II have restarted the program and indeed all settings are as you indicate. There is still no response to trying to scroll horizontally or vertically while "Fetch Last Page" is in progress.

I have checked what you have suggested and there is a major difference between V14 and V15 in this respect. Note that even in the simple case where I hit the Fetch Last Record button for a query that will return 10s of thousands of rows that the scroll bars don't work (or barely work) when the query is in process. This is with one connection to one session. Please help out here as I will have to roll back to V14 if this is not addressed.

I want to resurrect this issue as it has remained unsolved and it is really bothersome. In a long query (let's say returning 20000 rows) the horizontal and vertical scroll bars are inoperable. I have to wait until the query finishes to scroll the results. This is not what V14 did. Secondly, in a long query, I get no response when I click on the red hand in order to stop the query. I have set the Oracle preferences to Multi-session, and multiple connections are allowed.
Is there a difference between installing this for one user vs. all users on the machine. This is a Lenovo T series laptop running Windows 11.

To obtain some more diagnostic information, can you modify the PL/SQL Developer shortcut and add the DebugSQL parameter? For example:

"C:\Program Files\PLSQL Developer 15\plsqldev.exe" DebugSQL

Reproduce the problem, including the cancel button issue, and send me the debug.txt file that is generated in the %APPDATA%\PLSQL Developer 15 directory (e.g. C:\Users\<User>\AppData\Roaming\PLSQL Developer 15).

I sent you the Debug.txt in a pm.