The problems aren't expected to affect accuracy, and there weren't concerns about security. The Democrats first used a phone app to submit results in 2016.
This is a small problem in the long run. Most concerns about technology in the 2020 election revolve around more serious issues like voting system security and attempts to manipulate social media users. It's setting a not-so-positive tone for the election, though, and it won't be surprising if technical snafus pop up elsewhere on the road to the final vote on November 3rd.
Update (11:38 PM): And...now the results of the caucuses are delayed. However the reason for that delay is unclear. While at least one precinct secretary said live on CNN that "by all accounts the app doesn't work," a statement by the Iowa Democratic Party claims "This is simply a reporting issue. The app did not go down and this is not a hack or an intrusion." According to their statement, they are verifying with photos and a paper trail after "inconsistencies" appeared in three sets.