This one submarine was assumed there based on 6.Sept.1942 observation near island Verkkosaari? Unfortunately I didn't find any candidate from soviet submarines (looked mostly at M-class subs). Only starting with year 1943.
Anyway I don't think Sonderstaffel Buschmann was on Ladoga for anti-submarine activities. Probably they planned to use them as simple reconnaissance planes? And probably for Nordlicht? But either because operation was delayed/canceled or because of results (
always keine Feindbeobachtung) or because of submarine activity in Finnish Bay they were soon removed from Ladoga.
also looked thru KTB Skl Aug/Sep, nothing interesting there either.
LeLv 6 SPK contains one flight from Tallinn which is probably plane sent to Ladoga:
http://digi.narc.fi/digi/fullpic.ka?kuid=3608420