Major experience issues

Recently I had a lot of issues with this product, both in browser and in the app so here are all the details:
I have a certain folder where all of my biology flashcards are stored which were 4000 in number before the problems started. Till yesterday, I had practiced with spaced repetition daily and the number was somewhere around 800. Today morning while practicing rems in pc browser (through which i always access remnote), suddenly I faced intense lagging and the page became unresponsive and I had to kill it (and i was foolish enough to not take any screenshots). I tried reopening but the problem persisted.
Now I thought of opening the pc application which i had downloaded before but not used ever. After updating it from 1.3 to 1.5 and it syncing everything, the total number of cards randomly jumped to 4600 and the number of cards to be practiced went up to 1350. Moreover, the images in certain documents do not show up in the app and show only the broken picture emoji.
What I probably think has happened is that cards which I had already deleted have randomly decided to show up and also some exclusively forward or backward cards have changed to double sided ones.
I would want the remnote team to give me some reason as to why the lag happened and why in the world did i get 600 cards which were not present before.