Since installing LTR 5.4, which I've now upgraded to 5.6, I've encountered repeated slowness and malfunctions in operations, especially when using the Compare View function and the Tab key to open and close the right and left side panels. Such problems never arose during two years of using LTR-4 and nothing else has changed on my computer. I have a pretty simple system with only a few plug-ins, which are usually not in operation. I have 12GB of RAM in my Windows 7 PC. I could illustrate these problems with screen shots if you would tell me how to submit screen shots. Otherwise I will try to describe the problems in words.
The problem is clearly cumulative, growing worse as usage time passes. Compare View feature gradually slows down and eventually seems to choke as my work session proceeds. If I Exit LTR and re-enter and start all over, things will work normally for maybe 30 minutes, but then the Compare View feature begins to become very slow to respond. In a recent example with my screen full of thumbnails in Library mode I highlighted two images to compare. LTR started to open the Compare View screen by first having the top row of thumbnails disappear to be replaced by the "SELECT" and "CANDIDATE" words in their spaces (but no images), but Compare View never succeeded in gaining control of the screen. After some seconds the top row of thumbnails reasserted its position and the Compare View windows disappeared. But LTR kept trying to bring them back. Again the top row of thumbnails would go away, Select and candidate would reappear, try again, and give up. This went on for at least 2-3 minutes before I tried to choose File and Exit, but even that did not initially want to respond. It doesn't like to accept other commands when it's trying to open Compare View. Finally it allowed me to exit.
To experiment I created a new catalog of 1100 images. After 30-40 minutes, the Compare View function began to operate very slowly. With left and right side panels visible and two thumbnails highlighted, hitting Compare View can take half a minute before the two mid-size images open in their respective SELECT and CANDIDATE windows. When the side panels are open and two images are in the Select/Candidate spaces, hitting the Tab button to close the side panels produces a very delayed response--25-30 seconds to close them, a few more seconds to enlarge the two images to full size. To reverse the process (i.e., to recall the two side panels), hitting Tab would make the two sides of the screen go black for up to a minute, with no words visible. Eventually the info fields in the panels would open up.
I also created a new user account and imported a folder of 160 images. After half an hour Compare View began mis-placing data. (I have a screen shot to show this.) CANDIDATE appears on the left side of SELECT, whereas it should be on the right. The accompanying camera exposure data appears almost entirely to the left of the mid-screen dividing line. Although the Candidate and Select headings were transposed, the image exposure data was not, but the data for the image on the right was almost entirely to the left of the line dividing the screen in two.
Gurus in The Lightroom Forum have examined Task Manager data showing Processes running and Performance indicators and they see nothing wrong. I could also send screen shots of this data.
At this point, the only way I can process my images is to work 30-40 minutes and then shut down everything, exit, and re-start LTR. This is not normal. I hope you can find the cause, and then the solution. If you would like to see my screen shots, tell me how to submit them.