Version 2019.02 has been updated to use the latest Google Calendar and Google Contacts API libraries, which contain many corrections and improvements over the old versions of the libraries that were used in the previous version of VueMinder.
Syncing with Google Calendar and Google Contacts will be much more reliable in the latest version of VueMinder. For example, the latest Google Calendar API includes a "sync token" property which VueMinder can use for getting any events that have been modified since the last time the calendar was synced (incremental syncing). In the previous version, VueMinder kept track of the date and time (timestamp) the calendar was synced, and queried the Google Calendar API based on that timestamp. The problem with that approach is that if your computer clock is even a few seconds off, external changes in Google Calendar might not be detected and synced properly. The "sync token" property will work regardless of inaccuracies in your local clock and is a much more robust method of detecting external changes.
In addition, changes have been made in the latest version of VueMinder to reduce the number of queries against the Google Calendar API. VueMinder is constrained by a maximum daily quota on the number of queries. All users of VueMinder share this maximum quota. Due to the recent growth and popularity of VueMinder, this maximum quota has begun to be reached, resulting in several hours per day where VueMinder is unable to sync with Google Calendar (the quota resets each day at midnight Pacific Time).
We're working with Google to increase the quota, but since VueMinder is one of the largest users of the Google Calendar API, with a current maximum quota that far exceeds the quota allowed for most other programs, the process for getting the quota limit increased is taking longer than we'd like, and there's a chance Google will deny our request for a larger quota.
If enough people update to the new version of VueMinder, which reduces the number of queries, the maximum quota will be less of an issue. If the quota is still reached, the new version will show a message indicating how long it will take before syncing will start working again, instead of a generic error message that didn't provide any insight into the problem. If many people prefer to not update to the new version, then you may see this error message.