Well, the title is self explanatory. It can be tested with:
As long as it's broken other options than (the slow) ToExpression?
Stack Exchange cross-post link
Seems like Internal`DoubleToString also lost its definition. Maybe somebody from WRI can comment on it and maybe provide a replacement / workaround.
Thanks to b3m2a1: Internal`DoubleToString was renamed to Internal`MRealToString.