After trying many times to install apps such as LinuxTools, MemCached, etc. without success, I noticed that aaPanel did actually download and unzip the app into a temporary folder, but it did not complete the installation by moving the app folder to the /plugin folder.
The logs screenshot below show that FileManager downloaded and unzipped the file correctly, but then it did not actually install the app. I had to manually move the folder from /temp to /plugin to install the app. (See also the double slashes (//) that in my opinion are not correct).
