@techee I don't know if it's related at all, or if it could help in any way, but Chrome had a similar issue where it would open a new instance: "LaunchServices tries to open a second instance of Chromium". They committed a change with an attempt to fix this:
https://chromium.googlesource.com/chromium/src.git/+/fe15df9c055bb0c48e94aa915c5fde61ac84b03d -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://github.com/geany/geany/issues/1619#issuecomment-350762080
