I don't think this is the reason. I inspected other projects with similar support level and there was no significant change - growing projects kept growing and stable are stable.There are of cause also a world crisis to blame for this, since the patreon drop on 1st of April was the biggest in a very long time.
And you cant really blame people for this, since everybody is afraid, and some are even losing their jobs very sad times.
I can see two other reasons. Game is nearing its release - there is probably no flow of new supporters now as people will rather wait for the game to be released and grab it on steam. And there is no mention of getting full game if you support for x months on patron at all. Also no info that 1.0 is not the end of games development. (yea i know its on the link but not sure if people click it).
Second reason - making latest version public could have had upset some patrons.