Unable to add images (or other content blocks) to blog post

Site URL: https://www.andrewroosbell.com/blog

I just switched to Squarespace from Wordpress, and I imported all of my blogs, including their images. After I had imported them, the blogs appeared on Squarespace with the images as originally formatted. A couple of days later, after I had transferred the domain to Squarespace, the images in the blogs (not any other images on the site) had disappeared completely. 

Then, I tried to post a new blog containing an image, but I found there was no option to add an image content block (or any content block). I thought perhaps the problem was my template, so I tried to find a way to try a different one, but I couldn't find that either. 

Any help is appreciated. At this point I'm really baffled and kind of at a loss - I was hoping to get things up an running pretty quickly, and I made the switch largely because I had struggled a lot with issues at my previous host (I am not very tech-oriented). 

EDIT: I feel a bit silly, but I did just find the option to add an image block - I was really thrown by it being completely invisible, but it is there. The issue of the vanishing imported images is still outstanding, however.