I have same issue on my IPhone 6s, following are specifications and screenshot:
MM Server: 5.22.0, Build Hash 64922547a34fed47c045cc14273a8f86f0c1b9fa
MM Client: 1.30.1
iOS Sofware Version: 13.3.1
The problem happens once a week or once in two weeks, and I just keep reinstalling and asking people to send me messages. After enough tries, after I click on notification on my phone, application opens and everything works fine.
