45. Is it true the SDA Church teaches that Jesus’ 2nd coming has already happened, except that He came invisibly?

No. That is perhaps Jehovah Witnesses again, who believe Jesus has been ruling in heaven as King since 1914.

See: http://www.watchtower.org/e/bh/appendix_10.htm

And: http://en.wikipedia.org/wiki/Eschatology_of_Jehovah%27s_Witnesses

SDAs still await the literal and physical 2^nd coming of Jesus Christ – hence the name ‘Adventist’. People also probably confuse the SDA teaching about 1844, which in effect states Christ is involved in a pre-Advent Investigative Judgment as High Priest before His 2^nd Coming, in accordance with the book of Hebrews.