Yes. Check the following:

1) Coat with 0.1% gelatin for 1 hour in 37C before plating.

2) If it doesn't help, add Y27632 when plating, wait until they attach (about 2-4 hours), then replace the medium with a normal one.

3) If you can't buy Y27632, remove 2i from your media at the of plating, and add it only later, when cells already attach.

also check your plates cat number if they are not for suspension culture

1.Sometimes increasing the serum concentration in media also works.

2. Growing the cells in Rock inhibitor or blebbistatin also works but usually the media should be changed next day (without rock inhibitor or blebbistatin).

In my opinions, FBS of high quality is critical for the attachment of ESCs. 20% Australia FBS (gibco) is used in our medium. Moreover, check if your plates are non-treated which is recommended for suspended culture.

Can TC treated plates be used for gelatin coating or should the plates be untreated?

Massimo Bonora did you figure out how to attach the mESCs? I have been culturing mESC and using 0.2% gelatin for attaching the mESCs some of them attach however, most of them do not and they float to as debris turning the media yellow. Also i think the dead MEFs also float along with them.