As a FI you are PIC when instructing, that means that you must hold the ratings required to operate that class/type of aircraft. Keeping your FI rating valid requires two of these three options: 50 hours of instruction time, instructor refresher training, a profcheck. See FCL.940.FI FI –Revalidation and renewal (
https://www.easa.europa.eu/sites/def...-FCL-Aug20.pdf). If your previous revalidation included a profcheck, you can use hours and training this time.
The situation you're currently in is that your FI rating has not yet expired, but you are not able to exercise its privileges as the needed SEP rating has expired. (as stated in the previous post... I was busy typing
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