Keywords not attached to photos, missing collections

I bought a new hard drive.  After migrating all of my files from the old hard drive, I opened Lightroom Classic, opened my most recent catalog and imported my photos from the new hard drive.  I have 42,000+ photos.  And I now have 27,000+ photos with no keywords attached, that number used to be less than 800.  All of the filter collections I had set up are also missing.  Also, my flags, stars and color coding have disappeared from most of my photos.  Someone had suggested I may have opened the wrong catalog, but all of the recent keywords I had added to the keyword list are intact and the color codes I had renamed are also still present.  Two years ago, my old hard drive had crashed and I used the same process to set up Lightroom again and had no problems at all.  Of course, this was before the new Lightroom Classic.  So I don't know if I did something wrong, or it's a glitch in the new program.  Does anyone have any suggestions?  I really don't want to have to go through all of my photos and add keywords, flags and color coding all over again.  Any help would be appreciated, Thank you!