Version 13.0.5.1908. I am in Dual connection mode. When I using Log On/Off buttons in the session tab is pretty fast. When I connect or switch connections using the connections tree list it is very slow about 15 secs per window. Also if I close a window it could take up to 15 secs to close that window. I am sometimes waiting minutes, on closing the program or do a close all on all the windows.

I switched to single mode, have 4 files (SQL Windows opened), double clicked on a connection link in the Connections tree, it took about 41 secs to finish the connection. I had an wait cursor for about 30 secs, but the keys in the connection tree are flashing until 42 secs when it was done connecting.

Sometimes I have about dozens files opened and I would wait for minutes.

PL/SQL Developer
Version 13.0.5.1908 (64 bit)
Windows 10 Build 18362

Physical memory : 6,290,932 kB (4,110,892 available)
Paging file : 7,339,508 kB (5,397,036 available)
Virtual memory : 137,438,953,344 kB (137,434,132,212 available)

Parameters
C:\Program Files\PLSQL Developer 13\plsqldev.exe

Preferences
Session mode: Single
OCI Library: C:\Apps\Oracle\instantclient_12_2x64\oci.dll
Use OCI7: False
Allow Multiple Connections: True

Preference Files
C:\Users\felix\AppData\Roaming\PLSQL Developer 13\Preferences\default\Default.ini
C:\Users\felix\AppData\Roaming\PLSQL Developer 13\Preferences\felix\default.ini

License File
C:\Users\felix\AppData\Roaming\PLSQL Developer 13\aalf.dat

Debug file
C:\Users\felix\AppData\Roaming\PLSQL Developer 13\PlSqlDev.elf

Plug-Ins
*Active Query Builder (C:\Program Files\PLSQL Developer 13\PlugIns\ActiveQueryBuilder.dll)
*PL/SQL Documentation (plsqldoc) (C:\Program Files\PLSQL Developer 13\PlugIns\plsqldoc.dll)
(* is Active)

Homes

DLLs
C:\Apps\Oracle\instantclient_11_2\oci.dll

TNS File
C:\Apps\Oracle\network\admin\tnsnames.ora

Using
Home: C:\Apps\Oracle\instantclient_12_2x64
DLL: C:\Apps\Oracle\instantclient_12_2x64\oci.dll
OCI: version 12.1 (12.2.0.1.0)
Oracle Database 12c Release 12.1.0.1.0

Character Sets
Character size: 1 byte(s)
CharSetID: 46
NCharSetID: 871
Unicode Support: True
NLS_LANG: AMERICAN_AMERICA.WE8ISO8859P15
NLS_NCHAR_CHARACTERSET: UTF8
NLS_CHARACTERSET: WE8ISO8859P15

Process
Working Set = 165,593,088
Memory = 42,885,258
GDI Objects = 1525
User Objects = 774
Handles = 738

Monitor
PixelsPerInch = 96

Id = 0
PPI = 96
Primary = True
Handle = 65537
Left = 0
Top = 0
Width = 1920
Height = 1115

MainFormOnTaskbar = True

I upgraded to lastest PL-SQL Developer, change the ORACLE_HOME environment variable and upgraded to latest Oracle 19.3 instant client. Still slow. Tried with Dual Mode and Single Mode and Multi Mode. All modes are slow at connecting.

PL/SQL Developer
Version 13.0.6.1911 (64 bit)
Windows 10 Build 18362

Physical memory : 6,290,932 kB (4,112,500 available)
Paging file : 7,339,508 kB (5,414,248 available)
Virtual memory : 137,438,953,344 kB (137,434,132,816 available)

Parameters
C:\Program Files\PLSQL Developer 13\plsqldev.exe

Preferences
Session mode: Dual
OCI Library: C:\Apps\Oracle\instantclient_19_3\oci.dll
Use OCI7: False
Allow Multiple Connections: True

Preference Files
C:\Users\felix\AppData\Roaming\PLSQL Developer 13\Preferences\default\Default.ini
C:\Users\felix\AppData\Roaming\PLSQL Developer 13\Preferences\felix\default.ini

License File
C:\Users\felix\AppData\Roaming\PLSQL Developer 13\aalf.dat

Debug file
C:\Users\felix\AppData\Roaming\PLSQL Developer 13\PlSqlDev.elf

Plug-Ins
*Active Query Builder (C:\Program Files\PLSQL Developer 13\PlugIns\ActiveQueryBuilder.dll)
*PL/SQL Documentation (plsqldoc) (C:\Program Files\PLSQL Developer 13\PlugIns\plsqldoc.dll)
(* is Active)

Homes

DLLs
C:\Apps\Oracle\instantclient_19_3\oci.dll

TNS File
C:\Apps\Oracle\network\admin\tnsnames.ora

Using
Home: C:\Apps\Oracle\instantclient_19_3
DLL: C:\Apps\Oracle\instantclient_19_3\oci.dll
OCI: version 12.1 (19.3.0.0.0)
Oracle Database 12c Release 12.1.0.1.0

Character Sets
Character size: 1 byte(s)
CharSetID: 46
NCharSetID: 871
Unicode Support: True
NLS_LANG: AMERICAN_AMERICA.WE8ISO8859P15
NLS_NCHAR_CHARACTERSET: UTF8
NLS_CHARACTERSET: WE8ISO8859P15

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 13\plsqldev.exe" DebugSQL

Reproduce the problem and send me the debug.txt file that is generated in the "C:\Users\felix\AppData\Roaming\PLSQL Developer 13" directory.

I email the debug file to support