Thank you for your reply @Chin_Soon_Yeo
I could see that sub-folder q1gn4sygf4-staging.onrocket.site/ is no longer there on your Staging’s public folder.
I double checked further and just noticed these in your main.log file :
[2023-11-07 09:34:31.986] [warn] [terminalExec] Error: symlink has no referent: "/www/awonhubcom_389/public/wp-content/uploads/bb-platform-previews/b9014e776e469ca6dae702955bf32e95/d5f114d8e3c62f0810864354ff81f62f"
symlink has no referent: "/www/awonhubcom_389/public/wp-content/uploads/bb-platform-previews/b9014e776e469ca6dae702955bf32e95/ddd45c73825c4fae2bda3eda829176f6"
symlink has no referent: "/www/awonhubcom_389/public/wp-content/uploads/bb-platform-previews/b9014e776e469ca6dae702955bf32e95/161df2a04c3d2ee5292c4829583cb959"
symlink has no referent: "/www/awonhubcom_389/public/wp-content/uploads/bb-platform-previews/b9014e776e469ca6dae702955bf32e95/e06f90e20493fcdf4428111b4bd54dd0"
symlink has no referent: "/www/awonhubcom_389/public/wp-content/uploads/bb-platform-previews/b9014e776e469ca6dae702955bf32e95/a2ea15116725f93f1ad50491e3661c30"
symlink has no referent: "/www/awonhubcom_389/public/wp-content/uploads/bb-platform-previews/b9014e776e469ca6dae702955bf32e95/327b162a972ddf08c14d8e6b8db4e7d2"
symlink has no referent: "/www/awonhubcom_389/public/wp-content/uploads/bb-platform-previews/b9014e776e469ca6dae702955bf32e95/1a5ca6ad98de660088f772f9a5b895ec"
symlink has no referent: "/www/awonhubcom_389/public/wp-content/uploads/bb-platform-previews/b9014e776e469ca6dae702955bf32e95/657336e695e0f8e99fc66fad8954d661"
symlink has no referent: "/www/awonhubcom_389/public/wp-content/uploads/bb-platform-previews/b9014e776e469ca6dae702955bf32e95/5f7ebe93844853cf2ffce4cb8f803891"
symlink has no referent: "/www/awonhubcom_389/public/wp-content/uploads/bb-platform-previews/b9014e776e469ca6dae702955bf32e95/9b28dd1363d37e9864bd6c4c9c50b8e8"
and when I checked into your Staging account, indeed I noticed the same broken Symlink for those sub-folders:
So I think these broken Sylink (pointing to invalid/incorrect / non-exist files) were causing the import process to fail in DevKinsta.
I would suggest to check and remove those broken symlink files as shown in the above screenshot and give it another try. Hopefully that’s all and no more errors 
otherwise, you may want to send us your main.log again so we can check .
PS: and about this:
After each failed attempt, the website and control panel becomes very slow.
I don’t think it would affect your Staging site’s performance and/or the MyKinsta control panel to become very slow as DevKinsta shouldn’t affect them at all (it’s completely a separate program that runs on your local computer). If you’re experiencing slow access to your Staging site and/or with the MyKinsta control panel, please contact/reach out to our support team, so they can help to check and assist you further.
Best regards,
Agus