Andre
Google indexes all sorts of rubbish so it's probably not your content
I've noticed a multi will delay in recent months.. frustrating to be sure
What does search console tell you about an article's index status?
Is your sitemap submitted and being updated correctly?
What links have you created to your blog from high authority sites?
What is the blog about? Are there other bloggers in the same or connected topics who you could approach for links?
What links have you created from your blog to high authority sites?
That is, who are you quoting or referencing? What news or info sites are you looking back to do that Google can find you from there?
Are there sector related directories you can join that will give you a link?
Can you guest blog for friends or colleagues to get a link back?
Is your structure days set up?
Are you optimizing your titles and headings?
If you want to follow someone who speaks to this issue regularly, check Neil Patel out on Facebook, YouTube, etc. He's great
Just ideas
Be patient
Keep going
Have fun

Micha
"I don't know if it's because their website has a really low domain authority"
If you're talking about Google's index, they don't use domain authority and Google indexes many sites that have no inbound links pointing to them.
"it may be in googles' sandbox. "
Nope. The "sandbox" doesn't exist. Never did.
"I've heard that Google could be trying to tell me this content is garbage but the article are well researched and similar to search competitors on target keywords"
"Well researched" [in your or someone else's opinion] <> meeting Google's quality requirements.
"Is there any alarm bells I should be considering as to why I'm experiencing this issue?"
When submitting pages for indexing, do you get any CAPTCHAs?
Does Google say the pages are available but may not be indexed for [vague reasons]?
Does it take a long time for Google to respond when you submit a page for indexing?
Does Google tell you it can't crawl the site?
Does Google tell you it can't read the sitemap?
Those would all be "alarm bells" or similar in my book.
Ammon
Google doesn't worry about being fair to publishers. When you say "the article are well researched and similar to search competitors", you have to realize this is also saying "the content is essentially just the same that Google already have, but this one is ours", right?
Your content needs to be better than competitors to really provide value if Google already have their version. Now, 'better' gives a lot of leeway, many different directions in which to improve. It doesn't have to be longer, and in fact saying all the same more concisely might be 'better'. More citations and references to back up the article's opinions and conclusions would be 'better' too. And of course, almost everyone has heard of the 'Skyscraper Technique' of just adding more.
Google crawl and index according to an extremely complex prioritization algorithm that factors in the 'importance' of the site it is published on, the quality of the citations (links) pointing to it (including via internal links from other highly cited pages), whether keywords in the links or context of the links are trending or exceptionally popular at the moment, previous demand for content on this site (brand search etc), and finally, how long it has been waiting to be crawled.
Raising the site's perceived importance, especially through EARNED links from sites Google KNOWS can't be bribed or bought, helps the most.
For now it looks like you are making content faster than people are consuming it, and thus making a negative supply (of your pages) vs demand (for your pages) balance. Slow down the production of content to ONLY stuff that you are certain will gain huge traction, and especially will earn links you don't have to ask for.
Once Google determines that the demand for your content (via search and other metrics) is high enough, it will increase the priority for crawling your site and content. Scale up again slowly to keep the demand higher than the supply.
Morgan
I put my important links on a constant crawl. Let Google figure it out. I'll say this what I like to say a lot is, once you give Google what they want, things happen. Give Google what they like, things happen even faster.
I can't tell you how many fresh websites and sub-domains get indexed within a few days, and even more so with not so many posts.
Time to change our minds about the Google Sandbox. Dirt farmers live there.

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