Thumbnails stopped being created in Wordpress galleries, who knows what's the point?

Question

WordPress

I decided to put a simple site for a boutique alone, chose WordPress to make things go faster, everything was fine, but at one point the site stopped creating thumbnails for pictures, I used different plugins, at the moment I use this gallery , I don’t like it very much. Help me find a solution and advise the norms of the gallery? NextGEN Gallery installed and immediately crashed the site, in order to raise it, the plugin removed it ..