Scheduled uploads may not always trigger for extremely heavy users. This is not necessarily the fault of the uploader.
However, we still believe that 99.9% users should be just fine.
Depending on your Google account type, Google grants you certain amount “processing power” for running your custom scripts and add-ons across all your Google Sheets projects under your account.
For example, consumer accounts (@gmail.com) can currently run scripts and operations in add-ons for 90 minutes per day max and at the same time, the max run time of 1 operation is 6 minutes.
If you are using an enterprise account (usually running on custom domain), you are granted 6 hours of run time per day and one operation can run for up to 30 minutes.
These limits are changing in time, please refer to this official Google URL about the current quotas: https://developers.google.com/apps-script/guides/services/quotas
If you are already on the verge on hitting these limits even before you start using scheduler in the uploader, the scheduled uploads may not always run according to the schedule or different scripts and add-ons used in different files of yours may not operate according to the scheduler (if there is one).
Unfortunately, we cannot do anything about this otherwise we would have already fix it. We simply cannot adjust your Google quotas as much as we’d wish to. If you are running a free @gmail account, upgrading to the enterprise account will buy you more processing power – this is the only advice we can provide.