Another process, with id #######, is currently running ngcc

This happens when ngcc (Angular compatibility compiler) is not finished doing what it does, you must have enabled ivy in your Angular project. read here for more info about ivy.

1. First try to run npm install again, to see if it fixes your problem.
2. Try to run ngcc manually.
3. remove this file node_modules/@angular/compiler-cli/ngcc/__ngcc_lock_file__
4. If none of the above worked, then remove node_modules directory and try npm i again.

The Laptop Crashed and I got this problem after restart. Removing the below file from ionic project solved the problem.

node_modules/@angular/compiler-cli/ngcc/ngcc_lock_file

Try deleting your ngcc_lock_file in the path:

node_modules/@angular/compiler-cli/ngcc/ngcc_lock_file

It's work for me.