The logs are around 23MiB - I can send it directly to you if necessary (it is not really possible to anonymize everything…).
In what follows you see the downloaded JSON event, which is related to the error messages (“requesting calendar events for Google account”):
[D] unknown:0 - trace: " {"
[D] unknown:0 - trace: " \"kind\": \"calendar#event\","
[D] unknown:0 - trace: " \"etag\": \"\\\"3109858037332000\\\"\","
[D] unknown:0 - trace: " \"id\": \"_6pim8pj6cgsj6bb274q3ab9kckqj0b9pcgpmcb9iclh3ed1p70s3ie1pck_20090427T080000Z\","
[D] unknown:0 - trace: " \"status\": \"confirmed\","
[D] unknown:0 - trace: " \"htmlLink\": \"https://www.google.com/calendar/event?eid=XzZwaW04cGo2Y2dzajZiYjI3NHEzYWI5a2NrcWowYjlwY2dwbWNiOWljbGgzZWQxcDcwczNpZTFwY2tfMjAwOTA0MjdUMDgwMDAwWiB3b3NyZWRpaW5hbmF0b3VyQG0\","
[D] unknown:0 - trace: " \"created\": \"2009-03-18T17:19:01.000Z\","
[D] unknown:0 - trace: " \"updated\": \"2019-04-10T20:43:38.666Z\","
[D] unknown:0 - trace: " \"summary\": \"TITLE\","
[D] unknown:0 - trace: " \"location\": \"Auditorium Maximum\","
[D] unknown:0 - trace: " \"creator\": {"
[D] unknown:0 - trace: " \"email\": \"EMAIL\","
[D] unknown:0 - trace: " \"displayName\": \"NAME\","
[D] unknown:0 - trace: " \"self\": true"
[D] unknown:0 - trace: " },"
[D] unknown:0 - trace: " \"organizer\": {"
[D] unknown:0 - trace: " \"email\": \"EMAIL\","
[D] unknown:0 - trace: " \"displayName\": \"NAME\","
[D] unknown:0 - trace: " \"self\": true"
[D] unknown:0 - trace: " },"
[D] unknown:0 - trace: " \"start\": {"
[D] unknown:0 - trace: " \"dateTime\": \"2009-04-27T10:00:00+02:00\""
[D] unknown:0 - trace: " },"
[D] unknown:0 - trace: " \"end\": {"
[D] unknown:0 - trace: " \"dateTime\": \"2009-04-27T13:00:00+02:00\""
[D] unknown:0 - trace: " },"
[D] unknown:0 - trace: " \"recurringEventId\": \"_6pim8pj6cgsj6bb274q3ab9kckqj0b9pcgpmcb9iclh3ed1p70s3ie1pck\","
[D] unknown:0 - trace: " \"originalStartTime\": {"
[D] unknown:0 - trace: " \"dateTime\": \"2009-04-27T10:00:00+02:00\""
[D] unknown:0 - trace: " },"
[D] unknown:0 - trace: " \"iCalUID\": \"6edffd93-b945-4e50-9d3f-2eb74988989e\","
[D] unknown:0 - trace: " \"sequence\": 0,"
[D] unknown:0 - trace: " \"reminders\": {"
[D] unknown:0 - trace: " \"useDefault\": true"
[D] unknown:0 - trace: " }"
[D] unknown:0 - trace: " },"
1) Sync in calendar app: Afterward calendar app does not show any change.
[D] unknown:0 - debug: Event added remotely: "_ehqiqtj1cdgn8qbfdomkcb9i60o3ibpg6knj4c9d68o30e9f60qiuchh"
[D] unknown:0 - debug: Event added remotely: "_60q30c1g60o30e1i60o4ac1g60rj8gpl88rj2c1h84s34h9g60s30c1g60o30c1g8co3ad226p130di16sr46e9g64o30c1g60o30c1g60o30c1g60o32c1g60o30c1g6923gcpg8or32hhi6p1j6e1k8p13ce1j60o4ae1o6oqjegi48cog"
[D] unknown:0 - debug: not adding default reminder even though requested: not popup or invalid start offset.
[D] unknown:0 - debug: Event added remotely: "_60q30c1g60o30e1i60o4ac1g60rj8gpl88rj2c1h84s34h9g60s30c1g60o30c1g6go4cgpk74pjch1g6ook6e9g64o30c1g60o30c1g60o30c1g60o32c1g60o30c1g60q34dq384s44cq38d24ac1k70sk6d258crj0dhg8d0k8d226so0"
[D] unknown:0 - debug: not adding default reminder even though requested: not popup or invalid start offset.
[D] unknown:0 - debug: Event added remotely: "_60q30c1g60o30e1i60o4ac1g60rj8gpl88rj2c1h84s34h9g60s30c1g60o30c1g6go38h1g8cq4chhl71246e9g64o30c1g60o30c1g60o30c1g60o32c1g60o30c1g8cq34ea260rjgcpn6h2jccpk84s48cpl8cpk6d9j612j6g9j8opg"
[D] unknown:0 - debug: not adding default reminder even though requested: not popup or invalid start offset.
[D] unknown:0 - debug: Persistent occurrence added remotely: "_6pim8pj6cgsj6bb274q3ab9kckqj0b9pcgpmcb9iclh3ed1p70s3ie1pck_20090427T080000Z"
W] unknown:0 - ERROR: Cannot find parent event: "_6pim8pj6cgsj6bb274q3ab9kckqj0b9pcgpmcb9iclh3ed1p70s3ie1pck" for persistent occurrence: "_6pim8pj6cgsj6bb274q3ab9kckqj0b9pcgpmcb9iclh3ed1p70s3ie1pck_20090427T080000Z"
[D] unknown:0 - debug: Event added remotely: "_74s34dpo6sr3icg_20190101"
[D] unknown:0 - debug: Event added remotely: "_74p3echn6sqjgc0_20181226"
[D] unknown:0 - debug: Event added remotely: "_74r38e1o6oo3edg_20181225"
[D] unknown:0 - debug: Event added remotely: "_74ojce9p60r3ac8_20181026"
[D] unknown:0 - info : Error occurred while applying remote changes locally
[D] unknown:0 - info : performing ghost event cleanup
2) Snyc in Google-account settings: New events are added, existing ones are added too.
Note that there are many
Preformatted text
[D] unknown:0 - debug: not adding default reminder even though requested: not popup or invalid start offset.
D] unknown:0 - debug: not adding default reminder even though requested: not popup or invalid start offset.
[D] unknown:0 - debug: Event added remotely: "_60q30c1g60o30e1i60o4ac1g60rj8gpl88rj2c1h84s34h9g60s30c1g60o30c1g6go4cgpk74pjch1g6ook6e9g64o30c1g60o30c1g60o30c1g60o32c1g60o30c1g60q34dq384s44cq38d24ac1k70sk6d258crj0dhg8d0k8d226so0"
[D] unknown:0 - debug: not adding default reminder even though requested: not popup or invalid start offset.
[D] unknown:0 - debug: Event added remotely: "_60q30c1g60o30e1i60o4ac1g60rj8gpl88rj2c1h84s34h9g60s30c1g60o30c1g6go38h1g8cq4chhl71246e9g64o30c1g60o30c1g60o30c1g60o32c1g60o30c1g8cq34ea260rjgcpn6h2jccpk84s48cpl8cpk6d9j612j6g9j8opg"
[D] unknown:0 - debug: not adding default reminder even though requested: not popup or invalid start offset.
[D] unknown:0 - debug: Persistent occurrence added remotely: "_6pim8pj6cgsj6bb274q3ab9kckqj0b9pcgpmcb9iclh3ed1p70s3ie1pck_20090427T080000Z"
[W] unknown:0 - ERROR: Cannot find parent event: "_6pim8pj6cgsj6bb274q3ab9kckqj0b9pcgpmcb9iclh3ed1p70s3ie1pck" for persistent occurrence: "_6pim8pj6cgsj6bb274q3ab9kckqj0b9pcgpmcb9iclh3ed1p70s3ie1pck_20090427T080000Z"
[D] unknown:0 - debug: Event added remotely: "_74s34dpo6sr3icg_20190101"
[D] unknown:0 - debug: Event added remotely: "_74p3echn6sqjgc0_20181226"
[D] unknown:0 - debug: Event added remotely: "_74r38e1o6oo3edg_20181225"
[D] unknown:0 - debug: Event added remotely: "_74ojce9p60r3ac8_20181026"
[D] unknown:0 - info : Error occurred while applying remote changes locally
[D] unknown:0 - Exiting event loop
[D] unknown:0 - Stopping msyncd
[W] unknown:0 - Invalid reply for getSyncResults from plugin
[W] unknown:0 - Invalid reply for uninit from plugin
[D] unknown:0 - Stopping the OOP process for "google-calendars"
[D] unknown:0 - Process "/usr/lib/buteo-plugins-qt5//oopp/google-calendars-client" finished with exit code 2
Note that I have subscribed several own and shared Google accounts.