I've got CRS518-16XS-2XQ, CRS326-24S+2Q+R, XS+2733LC15D and MT-QSFP28-100-SFP28-28G-cnv-c. Firmware version of MT devices is 7.11.2.
I use QSFP to SFP28 adapter in CRS326. Auto negotiation is not working, link ok if only forcing 1G or 10G, but i need 25G.
Also SFP temperature monitoring alarming in log about overheating, SFP transceiver in QSFP to SFP adapter is slightly warm.

I use QSFP to SFP28 adapter in CRS326. Auto negotiation is not working, link ok if only forcing 1G or 10G, but i need 25G.

Just to be sure I got you right.

Are you trying to run the ports at 25 Gbps speed in the CRS326-24S+2Q+RM that only supports 24x 1/10 Gbps, 2x 40 Gbps ports?

From the brochure: “Overall it has two (2x) 40 Gbps QSFP+ ports and twenty four (24x) 10 Gbps SFP+ ports”

QSFP (4x10G) can't be converted to SFP28 (1x25G) of obvious reasons.