I'll give answering these a shot.
So, to start with a quick (well, "quick") background, the label "Zionist" is remarkably useless from a communication perspective. It can mean anything from:
wants there to be at least one country with no threat of discrimination for being Jewish
wants to ensure that Israeli citizens are safe from the surrounding countries who want to kill all the Jews and anyone standing too close
wants all Palestinian territory ceded to Israel and Palestinians wiped out
wants whatever's expedient to stop Israel getting bombed
wants all Jews to be in a little strip in the Middle East to bring about the end of the world - the "second coming," IIRC?
wants all Jews to be in a little strip in the Middle East to get them out of their country
wants all Jews to be in a little strip in the Middle East to make them easier to exterminate
wants to maintain a country to reliably flee to if/when their current country starts Holocaust 2: Here We Shoah-gain, without worrying about being turned away for being too many Jews
wants Netanyahu and his party to be able to do whatever they want
and many more. I admittedly hadn't heard your definition of Christian Zionism, as some sort of New Crusade for a Christian Jerusalem, but I wouldn't doubt people believe it. So in online discussions, you often wind up with exchanges like "I believe [nobody should kill all the Israelis]." "What? You want [all Gazans slaughtered, and the West Bank Palestinians too]? You monster!"
So, with that preamble, let's get into the meat of it:
The likely reason for bringing up Christian Zionists is because, well, it's a label that we simply never see. Despite, as the other person said, the entire global Jewish population being outnumbered by Christian self-described Zionists in the US alone, basically all accusations of zionism on tumblr are directed at Jews. We saw people saying "Happy Chanukah to all the non-zionist Jews!" but not "Merry Christmas but only to Christians who aren't zionists!" It's a frustration directed not specifically at you, but more at a general sort of collective of leftist goyish tumblr, which you happen to fit: people only think about zionism when Jews are involved, which is bigoted and also annoying.
This ties in nicely with your third point, actually:
I didn't want people to confuse my support of the Jewish community with support for the Israeli government.
Your followers would presumably have no issue if a post about protesters shutting down an anti-abortion event didn't include a caveat that you support pro-choice but not Israel. Hopefully, no callout posts will be made if you reblog a "happy easter" post without adding "but I don't condone the slaughter of Palestinians." Yet you worry that reblogging "I support the Jewish community" will have backlash from other users if you don't condemn Israel on it. Again, the topic of I/P only comes up when Jews are mentioned.
That also means that someone - possibly you, possibly your followers - believes that supporting Jews implies supporting Israel, that the default state for anyone who isn't bigoted against Jews is to cheer on the Israeli govt. And you did say that this is a new thing, that you reblogged it last year with no issue, which means that there's a growing trend of people who see "I support the Jewish community" and their first thought is "hmm, they must be evil."
This is... relatively easy to remedy, at least on a local-corner-of-tumblr level: stop bringing up Israel when Israel isn't mentioned. Over time, two things will likely happen: 1) your followers will see "Jews -> pro-Israel" less, and therefore themselves make the association less, and God willing it'll spread until the only people calling random Jews zionists are the people who would accuse us of being (((elite globalist lizard bankers))); and 2) you'll get the occasional ask demanding why you didn't denounce Israel in a "Jews are human actually" post, at which point you can try to explain that it's kinda bigoted to assume Jews and the Israeli govt think in lockstep (if you're up for it, of course - I admit the temptation to just block is pretty strong).
