Major This issue contains a number of points against WD08.
1) Line 1008 - the convention "24 (0x18) Byte Identifier of the Will Delay Interval" is used heavily in the document but it's really hard to read. There's no style applied to the text. Just making "24 (0x18) Byte" bold would help a lot, particularly when there's a list of identifiers and types.
2) Line 735, table 2.6. "Maximum QoS" is identifier 36 in the table and apparently applies to CONNECT and CONNACK packets. The description of CONNECT and CONNACK does not describe this identifier.
3) General - The language around request/response is hard to follow. The words "response" and "reply" probably have specific and different meanings, but it doesn't look like they're applied consistently throughout the document.
4) Line 1476, section 3.3.1.3 - The description of the various subscription options which affect retained messages is very hard to follow. Perhaps the complexity is justified (I'm not convinced), but it certainly needs writing in a way that an implementor has a hope of understanding. The "Retain Unavailable Advertisement" ought to be mentioned in section 3.3.1.3 since it negates the effect of marking a message as retained.
5) Line 898 - what on earth is a "reasonable" amount of time?
6) Line 993 - It seems very strange that the MQTT 5.0 specification describes the effect of hopping between MQTT 3.1.1 and 5.0.
7) Line 995 - "Clean Start" is called "Clean Session" in MQTT 3.1.1.
8) Line 1258 - It's not clear when a new session is considered to be established.
9) Line 2113, table 3.10 - Value 144 "Topic filter not valid" has the description "The topic filter is valid...." which is contradictory. The description could be improved.
10) Line 2273, table 3.13 - Value 140 description contains the term "user". This isn't an MQTT term - should it be "Session"?
11) Line 2934 - The sentence containing "Return code of 0x18 - Continue authentication" is difficult to read. It would really help to use a style other than normal text or perhaps quotes to indicate the name of the return code ("0x18 - Continue authentication").