I groan (inwardly) every time I see or hear the word syllabi at the law school where I teach.
Syllabus has become fully acclimatised and should go the way of normal English plurals: syllabuses.
In the same category is forum. Your Latin teacher (if you had one), would have insisted on the plural fora, of course. Both fora and forums are correct in English (although auto-correct wants to turn fora into for a).
Forums is preferable, and there is judicial authority for this view: see the words of Belobaba J in Leon v Volkswagen AG, 2018 ONSC 4265 at para 40 n 33.