Table 2.

Technical difficulties and consequences with regard to the digital symptom diary.

Description of technical issue	Patients affected, n	Consequence and solution, if applicable
Low internet connectivity hindered installation of the app during the screening visit	15	In most cases, the problem was solved by moving to a location with better internet connectivity or by postponing the installation to a later time.
Not receiving push-notifications as a reminder to complete the end-of-day questionnaires	12	In many cases, patients would complete the questionnaire regardless of receiving the notification. However, the exact effect is unknown, and it may have negatively impacted adherence during days that no notification was received. In most cases, the problem could be resolved by changing the telephone settings (eg by ignoring battery optimizations). In 2 cases in which the issue could not be resolved, reminders were given during the study period by setting the alarm of the device at 10 PM. In the short period during which it was unknown how many devices were affected, additional text messages were sent as reminders.
Incomplete views of the questions due to a too large scaling on smaller smartphone screens.	8	The issue was resolved by adjusting the scaling in the app during updates. Because only a few letters were not depicted correctly and because all participants had received a manual that included the actual questions asked, the negative effect of short-term scaling issues was estimated to be negligible.
iOS or Android updates that interfered with prior settings of the app	0	The issue did not lead to missing data because the small bugs did not shut down the app. The development team provided updates that resolved the issues as soon as possible.
Maintenance of the hosting server	21	The issue led to missing data of one complete day (ie, the day on which the maintenance took place) in all but 2 patients who were included at the time of the maintenance.