Thank you for reaching out to the Community! I do apologize that your email did not receive the open rate you were expecting. I do recommend taking a look at this helpful article on how to Improve Your Open Rates to see if any changes can be made. This article also includes tips on improving your sending reputation that may help! Thanks.
We have at times experienced the same thing but we have a relatively high open rate. We have found that we get a better open rate if we use a carefully worded subject line. I'm sure you already know that but sometimes they almost have to be a bit jolting. For instance, we've had events and people have told us in person they're attending but don't respond to an email or even open it when we use a line like Upcoming events...even Important Upcoming Events...but if we phrase the subject line as a question, we often get many more opens. For events, we might use Are you coming? sometimes even Are you coming or not? of course the body of the email has to be such that it is conversely but equally kind and uplifiting after a subject line like that, but they seem to do the trick. Also, subject lines like "You're in!" or "You are awesome!" etc. work well. It just takes a bit of round about thinking sometimes. I hope that helps a bit.
It sounds like you've already considered a lot of the best practices, @YvonneL99 . If you're concerned about your email getting to the inbox I'd also recommend looking into enabling email authentication. This is a way to help build a reputation as a trusted sender. This is more of a long term improvement where your reputation improves over time.
If you're experiencing a low open rate, there are a few additional things to consider: