Why a good answer sounds bad in English
Usually the content was fine and the delivery lost it. Four things do most of the damage, and none of them is vocabulary: hedging stacked up so a clear point sounds uncertain, describing your own work as helping somebody else with it, a story with no number or outcome in it, and apologising for your English before you have said anything.
Hedging
"Maybe I think it was probably a bit better" is four hedges around one claim. One is politeness and expected in many markets; three reads as not being sure about the content. Cut all but one and you have not changed what you said — you have let it be heard.
Handing your own work away
"I helped with the migration" puts somebody else in charge of it. If you did it, the verb is "I did". This is often modesty carried across from a culture where claiming individual credit is rude — and in a UK or US interview it costs you the level, not just the answer.
No evidence
"It went well" is a judgement. "It used to take two days and afterwards it took one" is evidence, and it contains no impressive number at all. Almost nobody actually lacks evidence — they have it and do not know it counts.
Apologising for your English
Native speakers ask for a question to be repeated constantly and never apologise for their English while doing it. Attaching the apology turns an ordinary request into an assessment of you, delivered by you, before the interviewer had formed one.
Have your own answer read — Paste or say an answer and get told which of these it is doing.
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