You entered the UK three times in less than three months. You spent just under 40 days there in all, in between hopping over to other European countries and apparently with no firm plan to return home since you did not have a flight booked when you returned for the third time.
In the eyes of the IO your pattern of travel looked unusual and it probably signalled that you don’t have a compelling reason to go back to Malaysia and that you may be attempting to use visa-free entry as a visitor to base yourself in the UK. The IO therefore concluded that you do not fulfil the ‘genuine visitor requirement’ of the Immigration Rules relating to visitors: https://www.gov.uk/guidance/immigration-rules/immigration-rules-appendix-v-visitor
- V 4.2. The applicant must satisfy the decision maker that they are a genuine visitor, which means the applicant:
(a) will leave the UK at the end of their visit; and
(b) will not live in the UK for extended periods through frequent or successive visits, or make the UK their main home;
You don’t explain in your question why you needed to travel to the UK so frequently. However, IMHO attempting to return to the UK as a visitor a little more than a month after having your third entry attempt curtailed is asking for trouble. It’s very possible that you would indeed be denied entry. If I were you I would change your travel plans for June to exclude the UK, and I would not attempt to return there for quite some time.