Stockfish is loading very slow

When I make a move at an analysis board, usualy stockfish shows the next move within one second, but every few moves it takes much longer (one minute or so). Then it shows only "engine is loading" for a long time. The same happens when I use the "Practise" feature and play against the computer, e.g. play K+Q vs K+R. Apparently it's not related on how difficult the position is, because it sometimes happens when there is only one legal move available.

I have found out that CPU utilization is up at 100% at this times. My PC is old and slow, but on the other hand when I use "request computer analysis" it runs quite fast.
And when I run Stockfish offline with SCID it ist very fast.

Is there some setting I can try to speed things up? Getting a move within a few seconds is more important for me than getting a very deep calculation.

Engine is loading ... Engine is calculating ...
Did the engine load? Or is it doing a deep analysis.

It could be nice to see: Infinite Analysis ... or Limited analysis ... , Instead of Engine is loading ...

If engine is continuously analyzing:
Go to your lower right menu analysis settings. If you want to limit your analysis depth, then click on that menu icon » Turn Infinite analysis off.

Note the engine will not move the pieces for you. Press the suggested co-ordinates and the pieces will move.

Thank you for the answer.
Is the engine loaded into my browser so that all the calculation is done on my PC or is the calculation done on the lichess server?
In the first case it might be faster and/or require less RAM if I would install Stockfish on my hard disk, but I don't know if there is a way to make Lichess run this one instead of loading it in the browser.