I'm doing the new training as a refresher course for myself to consolidate the learning completed last year. I'm occasionally getting stuck e.g. when having checked my work and got a "wrong" answer on the formatting or summary style I can't then get back to the answer to check a second time after correcting (the submit button does not re-appear). Leaving the outcome on a split screen the result from the first submit with the guidance what to correct disappears. I ended up today downloading the reference copy just to check my work. Any advice on how to stop this happening as I progress further into the course?
In many cases, the Check Your Work questions allow multiple "tries" to get to the correct answer, so if you initially select an incorrect response, just leave the tab open while you go back to your model to make corrections. When you are ready, come back to the Check Your Work tab, click Continue and select a new response. It sounds like that is what you are trying to do, but perhaps it is timing out and affecting your ability to view the question.
Another approach is to clear your cache, which will cause your browser to "forget" that you've already answered the Check Your Work question and allow you to try again from the beginning. To clear your cache in Chrome, for example, click the 3 vertical dots in the upper right corner, select More Tools, select Clear Browsing Data, and then select a relevant Time Range to clear the history for the Check Your Work answer in question (probably Last hour or Last 24 hours).