Good day!
I also have similiar to topic starter problem.
We are using PDF 24 8.6.1 version. OS is Windows 10 1709 16.29914
The steps to reproduce the problem:
Open PDF24 from tray icon or icon on desktop.
Run PDF Constructor from launcher.
Close the appeared window, and then try to open PDF Constructor.
This will result in nothing. Window with PDF Constructor won't open even. If you wait for some period of time it will open, but this period varies.
Process list in task manager will contain a PDF 24 Creator process as many, as you tried to open it.
Tried to reinstall, install latest version - no result.
Can someone help me to resolve this issue?