I am documenting this issue here since it drove me nuts and wasted a lot of searching time trying to find an answer on this forum, to no avail. I installed a package and it appeared to complete successfully. All files appeared to be in their correct locations but the block would not show up on the list of available blocks to install when I went to Add a Block. I discovered that in Dashboard, under Stacks & Blocks, I clicked on Block Types and there was my block. I clicked on it, opening a dialog page and then found and clicked on the Refresh button in the lower right corner. Something was amiss with the link to this block and clicking the Refresh button corrected it.

Hope this saves someone else some time!