I set the 'Accordion grouping' to 'Accordion content by grouped field' (first screenshot). After applying the settings and clicking the 'settings' link again, the previously selection is not shown - it defaults back to the 'One accordion item per result' option (second screenshot).
The selection was actually saved, but just not loaded when the settings modal is redisplayed.
Saving the view does make the setting persist.
1) For a Views Bootstrap display with format 'Bootstrap Accordion' click the format settings link
2) In the settings modal, select 'Accordion content by grouped field' for the Accordion grouping
3) Click Apply
4) Click the format settings link again
5) The Accordion grouping setting made previously is not loaded - the default One accordion item per result' option is selected
I will troubleshoot further when I have time.
Active
5.5
Accordion
MR! 54 resolves the reported issue by properly setting the default value of the "Accordion grouping" option.