"However, since the" is correct and usable in written English. You can use it to introduce a reason or explanation for something, either in the middle of a sentence or at the beginning of a sentence. For example, "The project was behind schedule. However, since the team was dedicated and motivated, they managed to finish it on time.".
However, since the strike began, Ms. Finke has published 142 posts about it.
However, since the advent of processed ready-meals, the amount we consume has fallen drastically.
However, since the CCTV inside the train was broken they were unable to pursue the investigation.
However, since the latter newspaper had already published a clarification, the watchdog required no further action.
However, since the beginning of the Putin era in 2000 the slide towards autocracy has accelerated.
However, since the accounts were filed, several high earners have been moved off the wage bill.
However, since the election, the issue seems to have been put on the back burner.
I love the desktop app, it’s always running on my Mac. Ludwig is the best English buddy, it answers my 100 queries per day and stays cool.
Cristina Valenza
Retail Lead Linguist @ Apple Inc.